Distribution Transformer VG PATEL TRANSFORMER ENCYCLOPAEDIA Distribution Transformer
Distribution Transformer VG PATEL
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer WHAT IS A TRANSFORMER? TRANSFORMER IS A STATIC DEVICE WHICH TRANSFORMS A. C. ELECTRICAL POWER FROM ONE VOLTAGE TO ANOTHER VOLTAGE KEEPING THE FREQUENCY SAME BY ELECTROMAGNETIC INDUCTION. Friday, September 10, 2021 PROF. V. G. PATEL 2
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer TYPES OF TRANSFORMER BY APPLICATION 1. DISTRIBUTION TRANSFORMER 2. POWER TRANSFORMER 3. CURRENT TRANSFORMER 4. POTENTIAL TRANSFORMER 5. FURNACE TRANSFORMER 6. BOOSTER TRANSFORMER 7. RECTIFIER TRANSFORMER 8. LOCOMOTIVE TRANSFORMER 9. MINING TRANSFORMER 10. PHASE SHIFTING TRANSFORMER 11. WELDING TRANSFORMER 12. HIGH VOLTAGE TESTING/SC TESTING TRF. 13. GROUNDING TRANSFORMERS 14. CONVERTER TRANSFORMER Friday, September 10, 2021 PROF. V. G. PATEL 3
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer The step down transformers used for electric power distribution purpose are referred as distribution transformer. There are several types of transformer used in the distribution system. Such as single phase transformer, three phase transformer, pole mounted transformer, pad mounted transformer, and underground transformer. Distribution transformers are generally small in size and filled with insulating oil. These transformers are available in the market in various sizes and efficiencies. Selection of distribution transformer depends upon the purpose and budget of the end users. Friday, September 10, 2021 4 PROF. V. G. PATEL
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer which is used for the purpose of distribution of power. Transformers with primary voltages of 3. 3, 6. 6, 11, 22 OR 33 k. V and secondary voltage of 400 OR 433 volt, 3 Phase (and 230 OR 250 volt single phase) are called Distribution Transformers. The maximum rating of these transformers for the purpose of this standard is considered up to 3000 k. VA, 3 Phase. Friday, September 10, 2021 PROF. V. G. PATEL 5
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer 11 KV/433 V is the standard voltage rating. IS-2026 is the NATIONAL INDIAN STANDARD. Standard KVA ratings are 25 KVA 63 KVA 100 KVA 160 KVA 200 KVA 250 KVA Friday, September 10, 2021 315 KVA 400 KVA 500 KVA 630 KVA 750 KVA PROF. V. G. PATEL 1000 KVA 1250 KVA 1500 KVA 2000 KVA 2500 KVA 3000 KVA 6
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer MAIN FEATURES v. OUTDOOR, OIL COOLED, 3 PHASE, 50 HZ v. PRIMARY IS DELTA CONNECTED AND SECONDARY IS STAR CONNECTED. v. NATURALY COOLED (ONAN TYPE). v. AMONGST ALL THE TYPES OF TRANSFORMERS THIS IS THE MOST REQUIRED AND MOST USED TYPE. Friday, September 10, 2021 PROF. V. G. PATEL 7
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer PARTS OF TRANSFORMER Friday, September 10, 2021 • • • • MAIN TANK RADIATORS CONSERVATOR EXPLOSION VENT LIFTING LUGS AIR RELEASE PLUG OIL LEVEL INDICATOR TAP CHANGER WHEELS HV/LV BUSHINGS FILTER VALVES OIL FILLING PLUG DRAIN PLUG CABLE BOX PROF. V. G. PATEL 8
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Difference between Power Transformer and Distribution Transformer Friday, September 10, 2021 PROF. V. G. PATEL 9
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer v Power transformers are used for transmission & receiving purpose, whereas distribution transformers are used only for distribution purpose. v Power transformer voltage ratio varies b/w 756 k. V to 11 k. V, Whereas distribution transformer voltage ratio varies b/w 33 k. V to 433 V. v Power transformers usually have higher MVA rating compared to distribution transformers. Friday, September 10, 2021 PROF. V. G. PATEL 10
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer To understand above, I want you to understand the different voltage levels which we use from starting of power generation till its distribution; 1. Generally electrical power is generated at low voltages i. e. 11 k. V. Large generators are designed to generate voltage ranging from 11 k. V to 28 k. V and frequency in 50 Hz or 60 Hz range. But To generate at 33 k. V, the size of the generator might be twice as large as the size of the 11 k. V generator. Friday, September 10, 2021 PROF. V. G. PATEL 11
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer 2. Now this generated energy is transmitted over the transmission lines of several hundred kilometers. When a current flows through a wire some energy is lost as heat. The higher the current, the more heat is lost. Hence we need to transmit the power at low current to minimize the conductor size and losses. To reduce the current we need to increase the voltage. In transmission/generating stations we use Step-up transformer to increase the voltage to say 220 k. V or above, these transformers are called as power transformers. Friday, September 10, 2021 PROF. V. G. PATEL 12
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer 3. Now this EHV transmission line terminates at local receiving station, where 220 k. V voltage is step down to say 33 or 11 k. V using the step down transformers, these transformers are also called as Power transformers. 4. Now, these 11 k. V voltage line is then distributed along every distribution station of the city, where voltage is further step down to 430 V AC using the step down transformer. Transformers used here are called Distribution transformers. Friday, September 10, 2021 PROF. V. G. PATEL 13
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Main Differences Power transformers are used in transmission net work of higher voltages for step-up and step down application (400 k. V, 200 k. V, 110 k. V, 66 k. V, 33 k. V) and are generally rated above 3 MVA. Distribution transformers are used for lower voltage distribution networks as a means to end user connectivity. (11 k. V, 6. 6 k. V, 3. 3 k. V, 440 V, 230 V) and are generally rated less than 3 MVA. Friday, September 10, 2021 PROF. V. G. PATEL 14
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Size / Insulation Level: Power transformer is used for the transmission purpose at heavy load, high voltage greater than 33 KV & nearly 100% efficiency. It also having a big in size as compared to distribution transformer, it used in generating station and Transmission substation and for high insulation level. The distribution transformer is used for the distribution of electrical energy at low voltage as less than 33 KV in industrial purpose and 433 v-220 v in domestic purpose. It work at low efficiency at 50 -70%, small size, easy in installation, having low magnetic losses & it is not always fully loaded. Friday, September 10, 2021 PROF. V. G. PATEL 15
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Iron Losses and Load Losses Power Transformers are used in Transmission network so they do not directly connect to the consumers, so load fluctuations are very less. These are loaded fully during 24 hr’s a day, so Load losses & Fe losses takes place throughout day the specific weight i. e. (iron weight)/(cu weight) is very less. The average loads are nearer to full loaded or full load and these are designed in such a way that maximum efficiency at full load condition. These are independent of time, so in calculating the efficiency only power basis is enough. Friday, September 10, 2021 PROF. V. G. PATEL 16
TRANSFORMER ENCYCLOPAEDIA Distribution Transformers are used in Distribution Network, directly connected to the consumer, so load fluctuations are very high. These are not loaded fully at all time so iron losses takes place 24 hr a day and cu losses takes place based on load cycle. The specific weight is more i. e. (iron weight)/(cu weight). Average loads are about only 75% of full load and these are designed in such a way that max efficiency occurs at 75% of full load. As these are time dependent, the all day efficiency is defined in order to calculate the efficiency. Friday, September 10, 2021 PROF. V. G. PATEL 17
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Power transformers are used for transmission as a step up devices so that the I 2 r loss can be minimized for a given power flow. These transformers are designed to utilize the core to maximum and will operate very much near to the knee point of B-H curve (slightly above the knee point value). This brings down the mass of the core enormously. Naturally these transformers have the matched iron losses and copper losses at peak load (i. e. the maximum efficiency point where both the losses match). Distribution transformers obviously cannot be designed like this. Hence the all-day-efficiency comes into picture while designing it. It depends on the typical load cycle, which it has to supply. Friday, September 10, 2021 PROF. V. G. PATEL 18
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Definitely Core design will be done to take care of peak load and as well as all-day-efficiency. It is a bargain between these two points. Power transformer generally operated at full load. Hence, it is designed such that copper losses are minimal. However, a distribution transformer is always online and operated at loads less than full load for most of time. Hence, it is designed such that core losses are minimal. In Power Transformer the flux density is higher than the distribution transformer. (For PT Approx. – 1. 4 Tesla, whereas for DT – 1 Tesla). Friday, September 10, 2021 PROF. V. G. PATEL 19
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Maximum Efficiency The main difference between power and distribution transformer is designed for maximum efficiency at 60% to 70% load as normally doesn’t operate at full load all the time. Its load depends on distribution demand. Whereas power transformer is designed for maximum efficiency at nearly 100% load as it always runs at nearly 100% load being near to generating station. Distribution Transformer is used at the distribution level where voltages tend to be lower. The secondary voltage is almost always the voltage delivered to the end consumer. Because of voltage drop limitations, it is usually not possible to deliver that secondary voltage over great distances. Friday, September 10, 2021 20 PROF. V. G. PATEL
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer As a result, most distribution systems tend to involve many ‘clusters’ of loads fed from distribution transformers, and this in turn means that thermal rating of distribution transformers doesn’t have to be very high to support the loads that they have to serve. Power transformers For transmitting networks of higher voltages for step-up and step-down application (400 k. V, 200 k. V, 110 k. V, 33 k. V) and are generally rated above 3 MVA in power transformers. For lower voltage distribution networks as a means for connecting end users among 11 k. V, 3. 3 k. V, 440 V, 230 V is basically rated less than 3 MVA in distribution transformers. Friday, September 10, 2021 PROF. V. G. PATEL 21
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Summarizing Friday, September 10, 2021 PROF. V. G. PATEL 22
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Power transformers are connected mainly in transmission network where they are basically used at higher voltage, while the distribution transformers are used in the distribution end hence they always face low voltage levels. Now coming to differencesv Since they are used in transmission network they are generally operated at > 33 KV while distribution transformers are generally connected at < 33 KV. v Due to the higher voltage rating the insulation level of the power transformers is very high while of distribution transformers is low. Friday, September 10, 2021 PROF. V. G. PATEL 23
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer v Load fluctuations are less in power transformers while they are more in distribution transformers as they are directly connected to load. v Power transformers are designed such that they can bear Cu loss and iron loss for 24 hours hence their cooling mechanism is very strong while in distribution transformers cu loss takes place based on load cycle while iron loss are always present. v While designing power transformers it is taken care that it's cu loss at full loading is less. While in distribution transformers, their iron losses are kept minimum. v In power transformers ratings are higher hence we use superior core as CRGO steel core while in distribution transformers amorphous steel is used. Friday, September 10, 2021 PROF. V. G. PATEL 24
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer v Since CRGO STEEL can carry more flux per unit weight hence specific weight of power transformers is less than that of distribution transformers. v Power transformers are designed to achieve maximum efficiency at full load. Hence according to the condition of maximum efficiency - full load copper loss of power transformers = iron loss. v While in distribution transformers we take that it is loaded up to 70 - 75 percent of rated output as average hence it is designed to achieve maximum efficiency at 70 - 75 percent hence according to the formula of maximum efficiency full load copper loss = 2* iron loss. Friday, September 10, 2021 PROF. V. G. PATEL 25
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Actually both are same. Distribution transformer generally used to provide voltage to consumers by stepping it down as voltage in feeders are quite higher for lossless transmission where as power transformers are electrical devices which are used to step up or down voltage and current. Distribution transformer is a special case of power transformer. There are many differences b/w these two transformer. But the major difference is the Maximum Efficiency E where power transformer is designed for maximum efficiency at 100% load and distribution transformer designed for maximum efficiency at 60% to 70% load. Friday, September 10, 2021 PROF. V. G. PATEL 26
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer TESTING OF TRANSFORMER TESTING IS CARRIED OUT AS PER IS-2026. ROUTINE, TYPE TESTS & SPECIAL TESTS ROUTINE TESTS ( TO BE CARRIED OUT ON EACH JOB) 1. Measurement of winding resistance 2. Measurement of insulation resistance 3. Sep. Arate source voltage withstand test (High Voltage tests on HV & LV) 4. Induced Over voltage Withstand test (DVDF test) 5. Measurement of voltage ratio 6. Measurement of No Load Loss & current. 7. Measurement of Load Loss & Impedance. (Efficiency & Regulation) 8. Vector Group Verification 9. Oil BDV test. 10. Tests on OLTC (if Attached) Friday, September 10, 2021 PROF. V. G. PATEL 27
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer TYPE TESTS THESE TESTS ARE CARRIED OUT ONLY ON ONE TRANSFORMER OF THE LOT. All routine tests Additionally following tests are included in type tests 1. Lightening Impulse test. 2. Temperature rise test Friday, September 10, 2021 PROF. V. G. PATEL 28
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer SPECIAL TESTS v Additional Impulse test v Short circuit test v Measurement of zero Phase sequence Impedance test. v Measurement of acoustic noise level. v Measurement of harmonics of the no load current. v Magnetic balance test. Friday, September 10, 2021 PROF. V. G. PATEL 29
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer TRANSFORMER SPEC. FOR SPECIFIC REQUIREMENT: v. KVA, v. VOLTAGE RATIO, v. INDOOR / OUTDOOR INSTALLATION, v. VECTOR GROUP, v. FREQUENCY, v. COOLING, v. TAPPING RANGE, v. TERMINATION REQUIREMENT FOR HV / LV, v. TEMPERATURE RISE OF OIL / WINDING , v. NO LOAD / LOAD LOSS, v. IMPEDANCE, v. PROTECTIVE ACCESSORIES, v. ANY OTHER SPECIAL REQUIREMENTS. Friday, September 10, 2021 PROF. V. G. PATEL 30
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer TRANSFORMER DESIGN STEPS: - v. Calculation of H. V. & L. V. current v. Calculation of volt per turn v. Calculation of core area and core diameter v. Select the winding v. Calculation of turns for H. V. & L. V. v. Calculation of conductor area & diameter v. Winding arrangement for H. V. & L. V. v. Calculation of the impedance of the winding v. Calculation of losses v. Calculation of core steps v. Calculation of tank height v. Calculation of gradient v. Calculation of radiator bank v. Calculation of efficiency at all loads Friday, September 10, 2021 PROF. V. G. PATEL 31
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer There are mainly 3 types of powers in case of AC circuit: 1. Active Power, P=VI*cos(phi) watt 2. Reactive Power, Q=VI*sin(phi) VAr 3. Apparent/Total Power, S=VI VA Friday, September 10, 2021 PROF. V. G. PATEL 32
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer There are three reasons why we rate transformer in KVA or MVA: 1. The transformer has to supply transfer both active and reactive power from one AC circuit to the other. And hence, it has to transform total power i. e. nothing but apparent power(S)=(P^2 + Q^2)^(1/2). The "S" is having unit of VA and hence transformers are rated in terms of KVA or MVA. 2. At the time of manufacturing of transformer it is not known that which type of load the transformer is going to serve (i. e. R, RL, RC or RLC or any other) hence its beneficial to rate it in terms of total apparent power "S". (KVA or MVA) 3. Transformer has two types of losses, *Copper loss, which are dependent on current (Current is having unit Ampere) *Iron losses, which are dependent on voltage (voltage is having unit Volts)Hence total losses=Iron Losses + Copper losses, which are dependent on VA. Friday, September 10, 2021 PROF. V. G. PATEL 33
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer MAINTENANCE OF TRANSFORMER Transformer is the heart of any power system. Hence preventive maintenance is always cost effective and time saving. Any failure to the transformer can extremely affect the whole functioning of the organization. Friday, September 10, 2021 PROF. V. G. PATEL 34
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer FAILURES & CAUSES v. Insufficient Oil level. v. Seepage of water in oil. v. Prolonged Over loading. v. Single Phase loading. v. Unbalanced loading. v. Faulty Termination (Improper sized lugs etc) v. Power Theft. v. Prolonged Short Circuit. v. Faulty operation of tap changer switch. v. Lack of installation checks. Friday, September 10, 2021 PROF. V. G. PATEL 35
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer FAILURES & CAUSES v. Faulty design v. Poor Workmanship v. Improper formation of core. v. Improper core bolt insulation. v. Burr to the lamination blades v. Improper brazing of joints. v. Burr /sharp edges to the winding conductor. v. Incomplete drying. v. Bad insulation covering. v. Insufficient cooling ducts in the winding. Friday, September 10, 2021 PROF. V. G. PATEL 36
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer FAILURES & CAUSES v. Bad Quality of raw material. v. Transit damaged transformers. v. After failure, transformer is removed and replaced with new/repaired one without removing the cause of failure which results in immediate or short time failure. Friday, September 10, 2021 PROF. V. G. PATEL 37
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer TROUBLE SHOOTING v High temperature v Winding Failure v Core Failure v High Exciting current v Audible internal arcing v Bushing flash over v Leakage through gasket / welding v Low oil alarm Friday, September 10, 2021 PROF. V. G. PATEL 38
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer TROUBLE SHOOTING v Oil sample failure v High acidity v Low IR value v Variation in the ratio v Frequent change in colour of gel v Presence of water inside the tank v Unusual noise v Relay not operating v OLTC failure Friday, September 10, 2021 PROF. V. G. PATEL 39
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Certain causes of failure of Transformers in service: v. Prolonged over heating v. Single phase loading v. Unbalanced loading v. Faulty termination v. Power theft and Hooking v. Wrong earth connection v. Prolonged short circuit v. Inadequate maintenance v. Operation of Tap switch on load v. Poor quality of LT cable v. Improper installation Friday, September 10, 2021 PROF. V. G. PATEL 40
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer Certain points to be remembered regarding basic characteristics of Transformer 1)Magnetizing current of central limb in core type construction will be 60 to 70% of that of extreme turn limbs. 2)Core bolt used in the yoke or leg lamination will be non magnetic steel used adequately insulated. 3)Yoke channels insulated from lamination, but earthed. 4)By varying voltage per turn and reactive length, variation in impedance is achievable. Friday, September 10, 2021 PROF. V. G. PATEL 41
TRANSFORMER ENCYCLOPAEDIA Distribution Transformer POINTS TO BE REMEMBERED v A transformer which has been commissioned and later withdrawn from service for any considerable time should be rechecked as when commissioned. v It is preferable not to mix oil from different suppliers. v IS : 335, IEC : 296 , BS : 148, etc. – Transformer oil v IS : 1886 – 1961 – Code of practice for maintenance of insulating oil v IS : 1886– 1967 – Code of practice for maint. of Trans. v IS : 2026, IS : 1180 – Transformer Friday, September 10, 2021 PROF. V. G. PATEL 42
TRANSFORMER ENCYCLOPAEDIA OPEN FORUM Friday, September 10, 2021 43
TRANSFORMER ENCYCLOPAEDIA THANQ Friday, September 10, 2021 44
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