Pokhara is the most beautiful city of
HEETS is the ISO 9001:2000 certified company. This company has adopted new technology in the field of electrical and electronics engineering with good quality management. The main focusing of this company is in the designing, manufacturing and repairing of electrical distribution transformer. Here in
Himalayan Electricals & Engineering Technology service Pvt. Ltd., HEETS a fully autonomous organization was established in 2003, with the commitment ensuring for the perfect and quality product in the field of electrical engineering and it has been achieving the determined goals successfully till date.
HEETS has a capacity to manufacture up to 630 KVA and up to voltage 33KV class distribution transformers and different size of welding machines.
A part from production of distribution transformers welding machines, HEETS serves the public in the field of repairing and maintenance of electrical device. Its plant at Pokhara, Western region of
The first product of HEETS was launched in April 2004. HEETS has been launching continuously its products from the date of establishment. Regular training is provided to employees of HEETS at all levels to keep pace with the changing technology and to upgrade its product.
Himalayan Electricals & Engineering Technology services has been exclusive in being offer products manufactured according to requirement and choice of customer in a clean, healthy and safe environment. Each incoming raw materials is carefully chosen, inspected and tested before it is used for long lasting products. Core laying, coil winding, tank fabrication and assembly each steps is carefully monitored by experts and tested by latest equipment of 21st century for quality and in accordance with the international standard. Thus, the long life durability of the product of HEETS is due to excellence technical side and having superior quality raw materials.
STANDARD
The distribution transformer shall be manufactured and tested in accordance with IEC (International Electro-technical Commission) set the international standard of "Distribution transformer" accepted internationally. The standards are set based on the experience of research institutions, working group of IEC manufactures and users. The standards are revised regularly on the basis of new experience of technology.
2. OBJECTIVE
The main objective of HEETS is to manufacture best quality of indoor and outdoor "Distribution Transformer" by using modern technology, selling in reasonable and competitive price with time delivery.
3. DEFINITION:
For the purpose of this standard the following definitions apply:
Transformer: Actually transformer is a static device. It operates on the principle of electro-magnetic induction, The transformer transforms alternating voltage and current applied at one winding into alternating voltage and current of the same frequency in the other or more windings, usually at different value of voltage and current.
a. Auto transformers: A transformer with at least two winding having a common part.
b. Oil – immersed type transformer: A transformer having its core and windings completely immersed in oil.
c. Dry type transformer: A transformer with core and winding not immersed in an insulating liquid.
d. Sealed type transformer: A transformer in which there can be no physical or chemical interchange between the atmosphere and its contents (i.e. non-breathing).
e. Winding: An assembly of turns constituting an electrical circuit associated with on of the voltage levels assigned to the transformer.
- High voltage winding: A winding associated with the highest operating voltage.
- Low voltage winding: A winding associated with the lowest operating voltage.
- Primary winding: A winding which receives power from the supply system.
- Secondary winding: A winding which delivers power to a system (load).
- Auxiliary winding: A winding intended to supply a small load in comparison with rated power of the transformer.
- Stabilizing winding: A delta connected auxiliary winding especially provided on star-star, star-zigzag or auto transformers to decrease the zero sequence impedance of the star connected winding (i.e. to facilitate flow of zero sequence current) there by reducing the magnitude of the third harmonic voltage and stabilize the neutral of the fundamental frequency voltage.
f. Terminal: A conducting element intended to receive external connections.
- Line terminal: A terminal intended for connecting a line conductor of the system.
- Neutral terminal: This is defined as:
* For a poly-phase transformer, the terminal connected to neutral point of a star-connected or zigzag connected winding.
* For a single phase transformer, the terminal for connections to a neutral point of a system.
g. Rating: Those numerical values assigned to quantities defining the operating limitations under the specified conditions.
- Rated quantities: Those quantities (voltage, current, power, etc.) the numerical value of which defines the rating.
- Rated primary voltage: The voltage assigned to be applied between the terminals of the primary winding of transformer with no tapping or to the principal tapping on a tapped winding.
- Rated secondary voltage: The voltage development between the terminals of secondary winding of a transformer at no load (if there are no tapping or in a taped winding when the tap is set to the principal tapping position) when rated primary voltage is applied to the primary winding.
- Rated voltage ratio: The ratio of the rated voltage of a winding to that of the another winding.
- Turns ratio: The ratio of the number of turns of one winding to those the another winding.
- Rated frequency: The frequency at which the transformer is designed to operate.
- Rated current: the line current derived by dividing the rated VA by the rated voltage and the phase factor.
h. Principal tapping: A tapping corresponding to the rated voltage of tapped winding.
- Plus tapping: A tapping so located in a tapped winding as to include this winding a greater number of turns than those corresponding to the principal tapping.
- Minus tapping: A tapping so located in the tapped winding as to include into this winding a lesser no of turns than those corresponding to the principal tapping.
- Step voltage: The difference between the tapping voltages of two adjacent tapping usually expressed as a percentage of the rated voltage.
i. Service conditions: Factors like altitude, air, temperature, humidity, etc. which may have influence on the performance of the transformer.
j. Temperature rises: The difference between the temperatures of the part of under consideration above which the temperature rises in measured.
k. Insulation level: That combination of the voltage values (both power-frequency and impulse) which characterizes the insulation of the transformer in respect of its capability of withstanding the dielectric stresses.
l. Uniformly insulated winding: A winding in which the insulation to earth at all points is designed to withstand the separate source-power-frequency test voltage appropriate to the line end.
- Graded insulated winding: A winding in which the insulation to earth is graded from the amount at the line end to a smaller amount at the neutral end so that the winding will withstand a separate source-power-frequency test voltage of a value appropriate only to the insulation level of the neutral end.
m. System nominal voltage: The RMS line to line voltage by which a system is designed.
- System highest voltage: The highest RMS line to line voltage that can be maintained under normal operating conditions at any time and at any point on the system. It excludes temporary voltage variation due to fault condition and sudden disconnection of large loads.
n. Exposed installation: An installation in which the transformer is exposed to the over voltage of atmospheric origin.
- Non-exposed insulation: An insulation in which the transformer is not exposed to the over voltage of atmospheric origin.
o. Star connection: The winding connection arranged in such a way that the phase winding of a three phase transformer or the windings for the same rated voltage of the single phase transformers constituting poly-phase bank is connected to a common neutral point and other end to the line terminal.
- Delta connection: The winding connection arranged in such a way that the phase winding of a three phase transformer or the winding for the same rated voltage of single phase transformers constituting a three phase bank are connected in series without closed circuit.
- Open delta connection: The winding connection arranged in such a way that the phase winding of a three phase transformer or the winding for the same rated voltage of single phase transformer constituting a three phase bank are connected in series without closing one corner of the delta.
- Zigzag connection: The winding connection in star of the phase windings of a poly-phase transformer, each phase of which is made up of parts in which the voltage induced are displaced in phase.
p. Phase displacement: The angular displacement between the vectors representing the voltage between the natural and the corresponding terminals of the higher voltage and lower voltage windings with a positive sequence voltage being applied to the higher voltage terminals. The phase displacement is expressed as clock hour figure.
q. Vector group symbol: A notation which indicates the connection of the high voltage, intermediate voltage (if any) and low voltage windings and their relative phase displacements.
r. Impedance voltage of two winding transformer: This is the voltage required to be applied at rated frequency to the winding of a poly-phase transformer when the terminals of the other winding are short circuited. Here reference temperature is 75 oC.
- Resistance voltage: The component of the impedance voltage in phase with the current.
- Reactance voltage: The component of the impedance voltage in phase with the current.
- Zero sequence impedance: The impedance that a symmetrical three phase circuit offers to the terminals of one of the windings, the remaining winding (s) being open circuited.
s. No load loss: The active power consumed when rated voltage at rated frequency is applied to the terminals of one of the windings, the remaining winding (s) being open circuited.
- No load current: The current flowing through the terminals of the winding of the transformer when rated voltage at rated frequency is applied, the other windings being open circuited. In tow winding transformers no load current is often expressed as a percentage of the rated current of the same winding.
- No load tap changer: A device for changing the voltage ratio of the transformer when the transformer is not loaded.
t. Routine test: A test made on each transformer.
u. Type test: A test made on a transformer which is representative of the other transformer to verify designed characteristics.
v. Acceptance test: Those tests carried out to the satisfaction of the purchaser to demonstrate that the transformer complies with the specification.
4. COMPONENTS OF HEETS TRANSFORMER
a. IRON CORE
Cold Rolled Grain Oriented (CRGO) magnetic Silicon steel sheet of high quality are used to make iron core. The iron loss and the no load current are decrease by making the flow of flux along the direction of grain orientation, which is done by mitred joints between core and yokes. The size of core and yoke are designed by considering technical as well as economical aspects.
b. HV AND
The type of winding chosen in such a way that the designed electrical characteristics and mechanical strength is obtained. The type and arrangement used for winding is chosen by considering the current rating, temperature rise, short circuit strength, impedance and surge voltage. Generally cylindrical, cross-over, continuous disc type winding are wound with continuous disc type winding are wound with constant tension directly on to a pressboard cylinder in HV side with enamelled insulated circular copper conductor. But in case of
c. CORRUGATED TANK
Tank bodies of the transformer are made from rolled steel plates. Which are fabricated to from a container with rigid bottom, corrugated sidewall and supper frame. The tanks are also provided with lifting lugs, oil drainage outlet, earthing connector. The internal surface of the the tank is varnished and the external surface are prepared for painting by sand blasting. The standard paint finish is a tow coat process of rust inhibiting primer followed by high specification finish coating. The tank provides structural strength to the complete product and enough to withstand stress produced during jacking and lifting. The complete designs of tank mainly focus on heat dissipation.
d. BUSHING
The shape and size of bushing used are depends on type (indoor or outdoor) and level of voltage. Bushing is used to prevent flashover between high voltage connections to the earthed tank. The HV bushing used are having capacity to withstand full wave impulse withstand voltage and basic impulse insulation level (BIL) as for IEC standard.
e. TAP CHANGER
The purpose of tap charger is to provide constant output voltage despite of the voltage fluctuation on the input system. Thus the voltage of power networks supplied by the transformer can be changed by changing the position of tap changer knob. The high voltage winding are provided with the toppings connected to an off -circuit tap changer mounted on the tank side and operated externally. The tapping position is fixed by lock system. Change of tapping is done manually.
f. OIL LEVEL INDICATOR
Each transformer is furnished with oil level indicator to indicate the level of oil inside the transformer tank. Oil level indicator attached on the side wall of transformer tank for the transformer having no conservator tank but it is attached on the side of conservator tank for the transformer having conservator tank.
g. CONSERVATOR TANK WITH DEHYDRATIONG BREATHER
Each transformer having size above 25 KVA is provided with conservator tank and dehydrating breather. Breather consist of silica gel granules. The granules in normal condition are blue and changes to pink when moisture is absorbed.
h. TRANSFORMER OIL
Transformer oil is one of the most import factor which determine the life and satisfactory operation of a transformer. Each transformer is supplied with high quality clean, dry and tested initial oil filling.
i. VACUUM DRYING
Before tanking, the core-coil assembly and tanks are placed in vacuum oven chamber to extract the accumulated moisture. Transformer is tanked and filled with purified and tested transformer oil immediately after drying.
j. ACCESSORIES
§ HV bushing with terminal connectors
§
§ Conservator tank (for conservator type transformer)
§ Dehydrating breather with silica-gel (for conservator type)
§ Tap changer
§ Oil level indicator
§ Lifting hooks
§ Corrugated tank Name plate with connection diagram
§ Name plate with connection diagram
§ Earth terminal
§ Oil drainage valve
§ Explosion vent (above 250 KVA)
§ Transport rollers (above 315 KVA)
Other additional accessories can be provided as per customer requirements.
5. LIMITS OF TEMPERATURE RISE
The loading to the transformer should be such that the limits of temperature rise of oil, winding and other parts determines the permissible load of a transformer.
(Above Ambient Temperature)
Top Oil 50o C
Winding 55o C
6. TRANSFORMER KVA RATING & TAPPING
a. Rating: Assigned values marked on the rating plate and will be such that the transformer can deliver its rated current under steady loading conditions without exceeding specified temperature rise limit on the rated voltage and the rated frequency.
Rated KVA: The product obtained by multiplying the rated voltage, the rated current and the appropriate phase factor given below:-
| No. of phase | Phase factor |
| 1 | 1 |
| 3 |
|
The rated KVA so assigned corresponds to continuous duty.
i. Standard KVA Rating:
Standard values of rated power for transformers shall be as given below:
- KVA rating for single phase transformer:
a. 5 KVA
b. 10 KVA
c. 15 KVA
d. 25 KVA
e. 50 KVA
- KVA rating for three phase transformer:
a. 25 KVA
b. 50 KVA
c. 100 KVA
d. 160 KVA
e. 200 KVA
f. 250 KVA
g. 315 KVA
h. 400 KVA
i. 500 KVA
j. 630 KVA
b. Tapping: transformer with tapping shall be stated if it is intended for off-load or for on-load tap changing. Unless otherwise specified, + 5% for the tapping range and 2.5% for the step voltages are assumed for the adjustments of the tapping. Tapping shall be provided on the high voltage side.
Tap changing shall be carried out by means of an externally operated-off circuit switch.
In case of transformer provided with on load tap changer, the number and the size of the steps and the corresponding voltages shall be as specified by the purchaser.
7. IDENTIFICATION ACCORDING TO THE COOLING METHODS
a. Identification symbols: Transformers shall be identified according to he cooling methods employed. Symbols used in connection with each cooling method shall be as given below.
| Letter symbols | |
| Cooling medium | Symbol |
| Mineral oil Synthetic insulating liquid Gas Waster Air Solid insulant | O L G W A S |
| Kind of circulation: | Symbol |
| Natural Forced | N F |
8. INSULATION LEVEL
a. Insulation Level: Several factors influencing the selection of insulation levels employed on transformers are:
i. highest system voltage
ii. system earthing
iii. degree of exposure to over voltage
b. The selection shall be based on the highest system voltages given below. If it is not specified, values given in the table assumed. The insulation level of a single phase transformer as a part of three phase bank shall be based on the highest system voltage of three-phase system.
Table:8.1
| Highest system voltage KV rms | Nominal system voltages KV rms |
| Less than 1.1 3.6 12 36 | Less than 1.0 3.3 11 33 |
9. RATING AND TERMINAL MARKING PLATES
i. Rating and terminal marking plates: Each transformer shall be fitted with three kinds of plates in a visible place:
a. rating plate
b. terminal marking plate
c. connection diagram
ii. Rating Plate: Each transformer shall be fitted with a rating plate of weather proof material giving the following information. :
a) Kinds of transformer
b)
c) Manufacturer's name, and country of manufacture
d) Manufacturer's serial number
e) Number of phases
f) Rated KVA
g) Rated frequency
h) Rated voltage ( voltage on no load on HV and
i) Rated currents (currents in HV and
j) Vector group symbol
k) Percent impedance voltage at rated current (measured value) at 75 oC.
l) Type of cooling
m) Weight of core and winding is kg
n) Weight of oil in kg
o) Volume of oil in litres
p) Total weight of transformer
q) Max. guaranteed temperature of oil in oC.
r) Max. guaranteed temperature of windings in oC.
s) Year of manufacture
t) Customer's reference number (if given)
10. Connection diagram: It shall furnish the following information:
a) the information given on the terminal marking plate;
b) the vector diagram and group no;
c) marking of sub terminals and tapping, if any together with an indication of their relative electrical position in the windings;
d) the information given on the rating plate;
e) the insulation level of each winding;
f) interconnection when three single phase transformers form a three-phase group.
a. Vector diagram: In vector diagram, the vector represents induced voltage and the counter clockwise direction of rotation. The phase voltage of the lower voltage winding and higher voltage are shown by vectors parallel to one another.
b. Connection of phase windings: In three-phase transformers, the connections of the higher voltage and lower voltage windings shall be indicated by the use of letters as given below.
| Winding connection | Type of connection | Designation |
| Higher voltage | Delta Star | D Y |
| Lower voltage | Delta Stare | d y |
The same shall also apply to the winding of the same voltage of single phase transformer arranged to form a three phase bank. If the neutral a star connected winding is brought out, indication shall be 'YN' and 'yn' for higher and lower voltage sides respectively.
c. Vector groups: There are four vector groups and each one includes three methods of connection of phase windings yielding the same phase displacement between winding. These are listed below:
| Group no. | Phase displacement in degrees | Clock hour no. |
| 1 2 3 4 | 0 180 -30 +30 | 0 6 1 11 |
Phase displacement: Phase displacement is the angular difference between the vectors representing higher voltage and lower voltage having the same marking letter, and the corresponding neutral points (real or imaginary).
A figure representing the hour indicated by a clock is adopted to indicate phase displacement where the minute hand represents the line to neutral voltage vector for the higher voltage winding end is set at 120 clock and the hour hand represents the line to neutral voltage vector for the lower voltage winding.
d. Vector relationships: The vector relating to the high voltage winding is always taken as the vector or origin. The group of connection and the phase displacement for two winding transformers are represented by three symbols, appearing in order where the first symbol indicates higher voltage, the second and third lower voltage connection ant the phase displacement expressed as the clock hour number.
11. TERMINAL MARKING
i. The letter used shall be:
a) for single phase transformer:
U: high voltage winding
u: low voltage winding
b) For a three phase phase transformer on a common core or on separate cores in a common tank:
UVW: high voltage windings
uvw: low voltage windings
ii. Neutral terminal: The neutral terminal shall be marked
N : When high voltage
n : When low voltage
12. ABILITY TO WITHSTAND SHORT CIRCUIT:
a. GENERAL: Transformers shall be designed to be capable of withstanding without damage the thermal and dynamic effects of external short circuit.
b. Over-current conditions: When external short circuit occurs on the system, the current rises to a certain value, this value of current is designed to be over current. Over currents are caused by three phase short circuit, line to line, double line to earth and line to earth faults.
c. Short circuit impedance: Typical value for the short circuit impedance for two winding transformers expressed as the impedance voltage at rated current and upper limit of over-current as a multiple of rated current at 75 oC shall be as 4% up to 100 KVA and 4.5% from 101-500 KVA & 5% above 500 KVA to 1000 KVA.
13. TESTING
The purpose of testing is to prove the validity of all technical data and to ensure the sound performance of the transformer. Every product of HEETS are subjected to different testing process for the verification of technical data. Routine and type tests mentioned below for each and every design of the distribution transformer.
a. ROUTINE TESTS
Routine tests are carried out on all transformers and involve the following measurements and inspection criteria.
§ Ratio test
§ Resistance Measurement
§ Polarity and phase relation test
§ No load loss test
§ Excitation current test
§ Impedance and load loss test
§ Applied potential test
§ Oil test
§ Insulation Resistance test
§ Leakage test
All transformers shall be subjected to routine tests:
The following shall constitute the routine tests:
a) Measurement of winding resistance
b) Ratio, Polarity and phase relationships
c) Measurement of impedance voltage/short circuit impedance and load loss.
d) Measurement of no-load losses and no-load current.
e) Insulation resistance
f) Induced over voltage withstand
g) Separate source voltage withstand
b. TYPE TESTS
§ Temperature Rise Test
§ Impulse test
§ Short Circuit Test
A transformer may be subjected to a range of tests for a variety of purposes. Tests shall be made at the manufacturer's works at any ambient air temperature below 45 oC.
Tests shall be carried out with all these external components and fittings, which are likely to affect performances in place. Unless otherwise agreed to between the manufacture and the purchaser and unless the test requires otherwise, tapped windings shall be connected on their principal tapping.
Unless the test clause states otherwise, the test basis for all characteristics except insulation shall be the rated condition. Where it is required test results shall be corrected to a reference temperature of 75 oC for class A of temperature class.
In addition to the routine tests, the following type tests shall be made by mutual agreement between the purchaser and the manufacturer.
a) Impulse voltage withstand test
b) Temperature rise test
f records of type tests on a transformer which is the representative of the one being purchased, are furnished, the purchaser may accept these as evidence of type tests instead of actual tests.
c. Special Tests:
If specified at the time of ordering, the following tests shall be made. (These tests, however, are not included in this standard)
a. Measurement of zero phase sequence impedance
b. Short circuit test
c. Dielectric test
d. Measurement of acoustic noise level
If the purchaser specifies the special tests other than those listed in 13.4, the test method shall be subject to agreement between the manufacturer and the purchaser.
d. Test Certificates:
The manufacture shall provide a certificate of all tests made on transformer.
e. Measurement of winding resistance (Routine Test):
The resistance of each winding, the terminals between which it is measured and the temperatures of the windings shall be recorded. Direct shall be used for the measurement.
In all resistance measurements care shall be taken to minimize the self inductive effects.
The time for the measuring current to be steady shall be noted during the cold resistance measurements and used for guidance when making hot resistance measurements following a temperature rise type test. This allows sufficient time for the inductive effects to disappear before the hot resistance measurements are made.
f. Oil immersed type transformers:
Before recording the resistance the transformer shall have been under oil without excitation for at least 3 hours to ensure that the windings are at the same temperature as the surrounding oil. Then the average oil temperature shall be taken to be the same as the average oil temperature.
g. Voltage ration measurement, check of Polarity & Phase Relationship:
The voltage ratio shall be checked on each tapping. The polarity of single phase transformer shall be checked. In case of 3-phase transformer, vector group symbol shall be checked.
h. Measurement of Impedance Voltage/short Circuit Impedance
The impedance voltage/short circuit impedance shall be measured at rated frequency with windings connected on the principal tapping using an approximately sinusoidal supply.
The measurement may be made at any current between 25% and 100% of the of the rated current. The preferred value shall not be less than 50% of the rated current. The measured values shall be corrected by increasing it in the ratio of rated current to test current.
i. Measurement of Load Loss
The load loss shall be measured at rated frequency with the windings connected on the principal tapping. An approximately sinusoidal supply is applied to one winding and other is short circuited. The load loss shall comprise of the sum of I2R loss in windings plus all stray losses. The measurement may be made at any current between 25% and 100% but preferably not less than 50% of the rated current. The measured value shall be corrected by multiplying it by the square of the ratio of rated current to test current. The measurement may be made at any temperature, but the results of tests shall be corrected to the reference temperature of 75oc assuming the I2R loss (R=
The resistance of the test connections should be sufficiently low not to affect the measurement.
j. Measurement of No-load loss and no load current:
The no-load loss and the no-load current shall be measured at rated frequency and rated voltage with the windings connected on principal tappings. If the test is performed on certain tappings other than principal tapping the value of voltage shall equal to the appropriate tapping voltage. An approximately sinusoidal supply is applied to one winding with other open circuited. Windings in open-delta connection shall have the delta closed.
For 3-phase transformers (without a delta connected winding) the voltage shall be measured by a voltmeter responsive to the RMS value of voltage wave. This voltage wave-form shall not contain fifth and seventh harmonics more than 5% of the RMS value of the applied voltage.
k. Measurement of Insulation Resistance:
The oil and winding temperatures shall be measured and recorded immediately prior to the test. The insulation resistance of each winding, in turn, to all the other windings, core and frame or tank connected together, and to earth shall be measured and recorded.
l. Induced over voltage withstand test:
An approximately sinusoidal alternating voltage shall be applied to the terminals of one winding of the transformer while the other shall be left open. The supply shall be at a greater frequency than the rated frequency to avoid excessive excitation current during the test.
The peak or RMS value of the induced voltage in the high voltage windings or applied voltage on lower voltage winding shall be measured. The RMS value (peak value divided by ) of the induced or applied voltage shall be twice the voltage appearing between those parts when rated voltage is applied between those parts when rated voltage is applied between the terminals or corresponding voltage is applied between a line terminal and the neutral terminal.
m. Separate source voltage-withstand test:
The separate-source voltage test shall be made with single-phase ac voltage of as nearly as sine wave-form and any convention frequency not less than 25 Hz. The peak value of he test voltage shall be measured and this value divided by shall be in accordance with tables: 8.2 & 8.3 (Section Eight).
The test voltage shall not be greater than one third of the test value and shall be increased to the increased to the specified value as rapidly as is consistent with its magnitude being indicated by the measuring instrument. At the end of the test, the voltage shall be reduced rapidly to less than on third of its full value before switching off.
n. Full wave impulse voltage withstand test:
Impulse test voltage shall be applied to the line terminals of the winding to be tested. The test shall be applied to each line terminal of a poly-phase transformer. The peak value of the applied voltage shall be that specified in Table: 12.2 (section 8). The wave shape shall be a standard wave having a front of 1.2 us and a time to half value of wave tail of 50 us. A tolerance of not more than 30% on the duration of the wave-tail is permissible, but where the characteristics of the transformer under test are such that it is impracticable to obtain the standard wave-shape within the above tolerances, for example, where the inductance of the winding is very low or its capacitance is very high, wider tolerances may be permissible by agreement between the manufacturer and its purchaser.
o. Impulse-voltage withstand test including chopped waves:
If specified by the purchaser as an addition to the full waves the sequence of voltage waves applied in turn to each line terminal of the transformer shall include two chopped waves.
The peak value of the voltage applied for the chopped waves shall be at least equal to the peak value of the specified full wave. The applied voltage shall be chopped on the wave-tail. The time to chopping shall be between 2us and 6us from the nominal start of the waves.
p. Test for temperature rise (type test):
- Measurement of temperature of cooling air: The cooling air temperature shall be measured by means of several thermometers (at least three) placed at different points around the transformer and at a level approximately half way up the cooling surface.
The thermometers shall be arranged at a distance of 1-2m from the cooling surface and they shall be protected from droughts and abnormal heat radiation.
When the transformer has forced air cooling the temperature of he air shall be taken at the intake to the cooler.
- Measurement of winding temperature:
The winding temperatures shall be principle be ascertained using the resistance method.
The temperature of a winding (T2 at the end of a test period shall be calculated from its measured resistance (R2 at that temperature and its measured resistance (R1), at some other temperature (T1) using the formula, valid for copper and aluminium:
The two methods shall not, in principal, be used concurrently.
- Measurement of top oil temperature:
The temperature of the top oil shall be measure by a thermometer placed in an oil-filled thermometer pocket.
- Duration of test:
The test shall be continued until one of the following requirements has been met. The method to be followed shall be chosen by the manufacturer.
Evidence shall be obtained that the highest temperature rise will not exceed the value given. If the test were continued until thermal equilibrium is reached. Temperature shall be taken where possible during operation as well as when the transformer is shut down. The test may be regarded as completed when the temperature rise does not increase by more that 3 oC in 1 hour.
- Loading oil-immersed type transformers:
§ Temperature rise tests include the following:
§ Determination of top oil temperature rise
§ Determination of winding temperature rises.
§ Determination of top oil temperature rise:
14. Progress record on manufacturing and repairing.
Actually the progress of HEETS is determined with the numbers of transformers repaired and supplied new transformers to customer. In fact Nepal Electricity Authority (NEA) is the main customer of HEETS. There are many districts and many villages where NEA has to distribute electric transmission line. NEA is also focused on distributing electric transmission line to lineless places in
a. NEW TRANSFORMER
| S.N. | KVA | RATING | TR. SR. NO. | NAME OF CLIENT | ISSUE DATE |
| 1. | 100 | 11/0.415 | 1001 | Pashchimanchal cold stores. | 2061/03/02 |
| 2. | 100 | 11/0.4 | 89/292(NPEC) | Rivan V. D. C. | 2061/03/13 |
| 3. | 100 | 11/0.4 | 1002 | Lamjung Electric Users Association | 2061/05/05 |
| 4. | 160 | 11/0.4 | 1005 | Kamana Roda Udyog | 2061/07/24 |
| 5. | 25 | 11/0.4 | B13856(GEC) | Dulegauda Electric Users Committee. | 2061/12/01 |
| 6. | 50 | 11/0.4 | 1003 | Harnampur Electrification Committee. | 2061/12/15 |
| 7. | 50 | 11/0.415 | 1004 | Kusma Electrification Committee. | 2061/12/15 |
b. REPAIR TRANSFORMER
| S.N. | KVA | RATING | TR. SR. NO. | NAME OF CLIENT | TR. NAME | R DATE | I DATE |
| 1. | 100 | 11/0.4 | No Nameplate | NEA Gagangauda | - - - - | 2060/08/18 | 2061/06/22 |
| 2. | 25 | 11/0.4 | 96.25.11.2526 | ,, ,, | NEEK | 2060/08/22 | ,, ,, ,, |
| 3. | 100 | 11/0.4 | -- -- -- -- -- | Base Camp Hotel | | 2061/01/25 | 2061/01/29 |
| 4. | 100 | 11/0.4 | 89100001 | NEA Pokhara | YIYANG | 2061/02/18 | 2061/03/11 |
| 5. | 100 | 11/0.4 | 89100045 | ,, ,, | ,, | ,, ,, ,, | 2061/03/12 |
| 6. | 50 | 11/0.4 | 94.50.11.142 | ,, ,, | NEEK | ,, ,, ,, | 2061/03/20 |
| 7. | 25 | 11/0.4 | 60.25.1999 | NTC Pokhara | Transweld | 2061/03/06 | |
| 8. | 150 | 11/0.415 | 214-150 | Hotel Barahi | ,, | 2061/03/19 | 2061/04/03 |
| 9. | 100 | 11/0.4 | 100/3679 | NEA Pokhara | ALFA | 2061/04/31 | 2061/06/27 |
| 10. | 200 | 11/0.4 | 86/1731 | ,, ,, | | 2061/04/31 | 2061/06/27 |
| 11. | 100 | 11/0.4 | 2002.100.11.5294 | ,, ,, | NEEK | 2061/04/31 | 2061/06/27 |
| 12. | 100 | 11/0.4 | 92/410 | NEA Baglung | NPEC | 2061/05/02 | 2061/05/23 |
| 13. | 50 | 11/0.4 | 95.50.11.729 | ,, ,, | NEEK | 2061/05/24 | 2061/06/11 |
| 14. | 50 | 11/0.4 | 257/50/052 | ,, ,, | NTPL | ,, ,, ,, | 2061/07/22 |
| 15. | 1500 | 33/11 | 520345/1975 | Baglung Sub- Station | -- -- -- | Home Service | 2061/06/14 |
| 16. | 50 | 33/0.4 | 0279/33/50/1995 | NEA Parwat | Precision | 2061/06/07 | 2061/09/06 |
| 17. | 25 | 11/0.4 | 54.25.11.1999 | NTC Pokhara | Transweld | 2061/06/22 | 2061/08/10 |
| 18. | 100 | 33/0.4 | 0257/33/100 | NEA Baglung | Precision | 2061/06/27 | |
| 19. | 150 | 33/0.4 | No Name Plate | NEA Baglung | --- --- -- | 2061/07/17 | 2061/07/24 |
| 20. | 100 | 33/0.4 | No Name Plate | NEA Baglung | -- --- --- | 2061/07/17 | ,, ,, ,, |
| 21. | 200 | 11/0.4 | 200.88.004 | APF TrainingCollage | NPEC | 2061/07/27 | 2061/08/27 |
| 22. | 50 | 11/0.4 | 1995.50.11.848 | Lamjung E. U. A. | NEEK | 2061/08/26 | 2061/09/06 |
| 23. | 200 | 11/0.4 | 1995.200.11.6672 | ,, ,, ,, ,, | --- --- ---- | 2061/09/05 | 2061/09/20 |
| 24. | 200 | 11/0.4 | 2001.200.11.5072 | ,, ,, ,, ,, | --- -- --- | 2061/09/06 | 2061/09/20 |
| 25. | 100 | 11/0.4 | 1999.100.11.4328 | ,, ,, ,, ,, | -- -- -- | 2061/09/08 | 2061/09/24 |
| 26. | 50 | 11/0.4 | 1995.50.11.647 | ,, ,, ,, ,, | NEEK | 2061/09/9 | 2061/11/17 |
| 27. | 1000 | 11/0.4 | --- --- --- | Manipal Teach.Hosp. | -- --- | Home Service | 2060/09/24 |
| 28. | 100 | 33/0.4 | 1997.100.33.3739 | NEA Beni | Precision | 2061/09/10 | 2061/09/27 |
| 29. | 300 | 11/0.4 | -- --- -- | | -- -- -- -- | Home Service | 2061/11/14 |
| 30. | 25 | 11/0.4 | 1996.25.11.2482 | NEA Parwat | NEEK | 2061/11/05 | 2061/11/29 |
| 31. | 100 | 33/0.4 | 0261.100.33.1994 | NEA Parwat | Precision | 2061/11/10 | 2061/12/15 |
| 32. | 25 | 11/0.4 | No Name Plate | NEA Syangja | -- -- -- | 2061/12/05 | 2062/12/20 |
| 33. | 50 | 11/0.4 | No Name Plate | NEA Tanahun | FTS | 2062/01/05 | 2061/01/19 |
| 34. | 25 | 11/0.4 | 98363 | ,, ,, | FTS | 2062/01/05 | 2062/01/19 |
| 35. | 50 | 33/0.4 | 1999.50.33.4187 | NEA Syangja | NEEK | 2062/01/06 | 2062/01/20 |
| 36. | 50 | 11/0.4 | 50-57 | NEA Malepaten | ALFA | 2062/01/06 | 2062/01/20 |
| 37. | 200 | 11/0.4 | 1997.211.3648 | ,, ,, | NEEK | 2062/01/07 | 2062/01/20 |
| 38. | 100 | 11/0.4 | 61.100.050 | Grihalaxmi Gas. | NPEC | 2062/02/07 | No /02/08 |
| 39. | 100 | 33/0.4 | 0264.100.33 | NEA Beni | Precision | 2062/02/08 | |
| 40. | 25 | 11/0.4 | 1996.25.2468 | NEA Syangja | NEEK | 2062/02/10 | 2062/02/16 |
| 41. | 50 | 11/0.4 | 98122 | NEA Syangja | FTS | 2061/11/21 | 2061/12/20 |
| 42. | 25 | 11/0.4 | 001/7 | NEA Syangja | Chinese | 2062/02/20 | |
| 43. | 25 | 11/0.4 | 102.25.058 | NEA Syangja | ETPL | 2062/02/26 | 2062/03/11 |
| 44. | 25 | 11/0.4 | 22.25.11.4026 | NEA Syangja | NEEK | 2062/01/20 | 2062/02/01 |
| 45. | 25 | 11/0.4 | 2002.25.11.5754 | NEA Syangja | NEEK | | |
| 46. | 100 | 11/0.4 | 98165 | NEA Tanahun | FTS | 2062/02/06 | 2062/02/21 |
| 47. | 50 | 11/0.4 | 98314 | NEA Tanahun | FTS | 2062/01/05 | 2062/01/22 |
| 48. | 25 | 11/0.4 | 2004.25.11.6712 | NEA Tanahun | NEEK | 2062/01/20 | 2062/02/21 |
| 49. | 15 | 11/0.23 | 2002.15.11.559 | NEA Tanahun | NEEK | 2062/01/07 | 2062/01/22 |
| 50. | 150 | 33/0.4 | 003.150.045 | NEA Parwat | NTPL | 2062/01/09 | 2062/02/11 |
| 51. | 25 | 11/0.4 | 25.3065 | NEA Parwat | ALFA | 2062/01/10 | |
| 52. | 50 | 33/0.4 | P/50/2005 RH | NEA Parwat | Precision | No /01/24 | 2062/02/16 |
| 53. | 150 | 33/0.4 | No Name Plate | NEA Beni | Precision | | |
| 54. | 50 | 11/0.4 | 90/452 | NEA Gagangauda | NPEC | | |
| 55. | 50 | 11/0.4 | 5190177 | NEA Gagangauda | Stromberg | 2062/03/21 | 2062/04/04 |
| 56. | 50 | 11/0.4 | 90/411 | NEA Gagangauda | NPEC | 2062/03/05 | 2062/03/20 |
| 57. | 50 | 11/0.4 | 851132 | NEA Gagangauda | Korian | 2060/03/05 | 2062/03/15 |
| 58. | 100 | 11/0.4 | 1996.100.11.1960 | NEA Pokhara | NEEK | 2062/02/12 | 2062/02/27 |
| 59. | 25 | 11/0.4 | 2001.25.11.4617 | NEA Pokhara | NEEK | 2062/02/12 | 2062/02/27 |
| 60. | 200 | 11/0.4 | 89-974 | NEA Pokhara | | 2062/02/12 | 2062/02/27 |
| 61 | 100 | 11/0.4 | 11/3679 | NEA Pokhara | ALFA | 2062/02/20 | 2062/03/15 |
| 62 | 100 | 11/0.4 | 89100010 | NEA Pokhara | YIYANG | 2062/03/01 | 2062/03/16 |
| 63. | 25 | 11/0.4 | 2004.25.11.6712 | NEA Tanahun | NEEK | No /03/01 | 2062/03/12 |
| 64. | 250 | 11/0.4 | 10666 | K.C. Construction | Jonson E. | 2062/03/02 | 2062/02/17 |
| 65. | 100 | 11/0.4 | 89100026 | NEA Pokhara | YIYANG | 2062/03/13 | 2062/03/28 |
| 66. | 25 | 11/0.4 | 25.60.1999 | NTC Pokhara | Transweld | 2062/03/13 | 2062/03/28 |
| 67. | 50 | 11/0.4 | 1994.50.11.384 | NEA Syangja | NEEK | No /03/19 | 2062/04/06 |
| | | | | | | | |
| | | | | | | | |
TRANSFORMER POWER LOSSES
| Power (KVA) | Phase | Voltage System 11000-230 Losses (Watts) | % Impedance | Total Weight (Kgs) | |
| No Load Losses | Load Loss at 75oC | ||||
| 5 | Single | 10 | 130 | 2.8 | 90 |
| 10 | Single | 75 | 280 | 2.8 | 110 |
| 15 | Single | 80 | 360 | 2.9 | 140 |
| 25 | Single | 130 | 490 | 2.9 | 200 |
| 50 | Single | 200 | 840 | 3.0 | 260 |
VOLTAGE SYSTEM (11000/400, V & 33000/400,V)
| Power (KVA) | Phase | Losses (watts) | % Impedance | Total Weight (Kgs) | |||
| No Load Losses | Load Losses at 75oC | | | ||||
| 11kV | 33kV | ||||||
| 25 | 3 Phase | 120 | 150 | 475 | 4 | 310 | 540 |
| 50 | 3 Phase | 180 | 240 | 1050 | 4 | 440 | 610 |
| 100 | 3 Phase | 280 | 320 | 1750 | 4 | 700 | 910 |
| 160 | 3 Phase | 440 | 510 | 2300 | 4 | 940 | 1160 |
| 200 | 3 Phase | 480 | 530 | 2875 | 4 | 1100 | 1300 |
| 250 | 3 Phase | 640 | 700 | 3300 | 4 | 1300 | 1450 |
| 315 | 3 Phase | 700 | 740 | 3950 | 4 | 1460 | 1700 |
| 400 | 3 Phase | 800 | 860 | 4600 | 4 | 1640 | 1900 |
| 500 | 3 Phase | 900 | 1050 | 5500 | 4 | 1900 | 2200 |
| 630 | 3 Phase | 1170 | 1240 | 6650 | 4 | 2260 | 2560 |
These figures approximate for estimation purpose for silicon steel core type distribution transformer.
