An Article For You to Understand Transformer Nameplate

transformer nameplate1

As such an important piece of electrical equipment, do you ever get confused when you see the Coal Mine Transformer nameplate and hear the various equipment parameters details? If the answer is yes, then the following is a shallow analysis of these issues and popularize the transformer nameplate information.

When working in the system, the power transformer can transmit the electrical energy from its primary side to the secondary side through the conversion of electromagnetic energy, while increasing or decreasing the voltage according to the needs of transmission and distribution. Therefore, it plays a very important role in the whole process of production, transmission and distribution of electrical energy. In the whole power system, the capacity of transformer is usually about three times more than the capacity of generator.

Transformer in the specified use environment and operating conditions, the main technical data are generally marked on the name plate of transformer. Mainly including: rated capacity, rated voltage and its tap, rated frequency, winding coupling group and rated performance data (impedance voltage, no-load current, no-load loss and load loss) and total weight.

Table of Contents

How to check the model number of the transformer?

name plate of transformer2

In the name plate of transformer, the model number of the transformer is divided into two parts. The first part consists of the letters D and S, representing the category, structural characteristics and use of the Coal Mine Transformer. The latter part consists of numbers, indicating the capacity (KVA) and high voltage winding voltage (KV) level of the product.

The letter meanings are as follows.

● Part 1 indicates the number of phases

D-single-phase (or forced-directed); S-three-phase

Part 2 indicates the cooling method

J-Oil-immersed self-cooling; F-Oil-immersed air-cooling; FP-Forced oil circulation air-cooling; SP-Forced oil circulation water-cooling.

●Part 3 indicates the number of voltage levels

S-Three-stage voltage; no S means two-stage voltage

●Other: O-full insulation; L-aluminum coil or lightning protection; O-autotransfer (in the first place indicates buck autotransfer, in the last place indicates boost autotransfer); Z-voltage regulation; TH-moist heat tape (protection type code) TA-Dry heat belt (protection type no-load current type code)

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What is the rated capacity (kVA)?

transformer nameplate information3

Rated voltage. Rated current under continuous operation, the capacity that can be delivered. Rated capacity is the guaranteed value of the apparent power output of the Coal Mine Transformer under rated operating conditions (i.e., operating conditions at rated voltage, rated frequency, and rated use conditions) as specified by the manufacturer, expressed as SN.

Rated capacity usually refers to the capacity of the high-voltage winding; when the transformer capacity is changed due to the cooling method, the rated capacity refers to its maximum capacity.

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What is the rated voltage (kV)?

The working voltage that a transformer can withstand when operating for a long time. In order to adapt to the needs of grid voltage changes, transformers have taps on the high voltage side to adjust the output voltage on the low voltage side by adjusting the number of turns on the high voltage winding. The rated voltage of the Coal Mine Transformer is the rated voltage of each winding, which is the rated applied or no-load voltage generated.

The primary rated voltage U1N is the rated voltage value received at the end of the primary winding of the transformer; the secondary rated voltage U2N is the voltage of the secondary winding (in V or KV) when the primary winding is connected to the rated value and the tap changer is placed at the rated tap position, and the transformer is unloaded. The rated voltage of the three-phase transformer refers to the line voltage.

In general, the appropriate tap is drawn on the high-voltage winding, because the high-voltage winding or its separate regulating winding is often set at the outermost, leading to a convenient tap; secondly, the high-voltage side of the current is small, leading to the tap lead and tap changer current-carrying part of the small cross-section, the tap changer contact part is easy to solve.

As an example: Dry-type transformer nameplate

current transformer name plate details4

The meaning of “SCB10-1000KVA/10KV/0.4KV” dry-type transformer is as follows
●S means this transformer is a three-phase transformer, if S is replaced by D, it means this transformer is single-phase.
C means the winding of dry type transformer is resin casted solid.
●B means foil winding, if R means winding winding, if L means aluminum winding, if Z means on-load regulator (copper is not marked).
●10 indicates the design serial number, also called the technical serial number.
●1000KVA means the rated capacity of this transformer (1000 kVA).
●10KV means primary rated voltage, 0.4KV means secondary rated voltage.

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What is the rated current (A)?

Coal Mine Transformer in the rated capacity, allowed long-term through the current. Transformer one or two rated current is the line current that is allowed to pass through the transformer winding for a long time under the rated voltage and rated ambient temperature so that the transformer parts do not exceed the temperature, the unit is expressed in A.

What is no-load loss (kW)?

The active power drawn when the rated voltage at the rated frequency is applied to the terminals of one winding and the rest of the winding is open circuit. It is related to the core silicon steel sheet performance and manufacturing process, and the applied voltage.

The active component I0a of the no-load current is the loss current, and the active power drawn from the power supply is called no-load loss P0. The no-load loss is mainly determined by the unit loss of the core material.

What is no-load current (%)?

When the transformer is unloaded at rated voltage on the secondary side, the current passed in the primary winding. Generally expressed as a percentage of the rated current. Transformer primary side applied (rated frequency) rated voltage, the secondary side disconnected operation is called no-load operation, when the primary winding through the current called no-load current, it is mainly used only to generate magnetic flux to form a counter-electromotive force to balance the voltage applied outside, so no-load current can be seen as also is the excitation current. The transformer capacity, magnetic circuit structure and the quality of the silicon steel sheet are the main factors that determine the no-load current.

What is the load loss (kW)?

The power consumed by the transformer when the secondary winding of the transformer is short-circuited and the rated current is applied to the rated tap position of the primary winding.

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What is the impedance voltage (%)?

Short-circuit the secondary winding of the Coal Mine Transformer, slowly increase the voltage in the primary winding, when the short-circuit current of the secondary winding is equal to the rated value, then the voltage applied to the primary side. Generally expressed as a percentage of the rated voltage.

What is short circuit impedance?

Impedance voltage, also known as short-circuit voltage (Uz%), it means that the transformer through the rated current in the transformer’s own impedance of the voltage loss (percent).

It is obtained by test as follows.

The transformer secondary side short-circuit, in the primary side gradually apply voltage, when the secondary winding resistance through the rated current, the primary winding resistance applied voltage Uz and the rated voltage Un ratio of percent, that is: Uz% = Uz / Un × 100%.

In normal operation, the impedance voltage is less better, because when the impedance voltage is too large, it will produce too large a voltage drop, and in the transformer when a short circuit occurs, the impedance voltage is larger than better, because it can limit the short circuit current, otherwise the transformer can not withstand the short circuit current impact.

Keep on reading What is the no load losses of transformer?What is the short-circuit loss of the transformer

What is short-circuit loss?

Short-circuit loss transformer secondary side short-circuit, primary winding through the rated current when the transformer by the power drawn (also known as consumption of) power (unit W or KW).

What is the connection group on the transformer nameplate?

It indicates how each phase of the Coal Mine Transformer winding is connected and the phase relationship between the primary and secondary line voltages. The sequence of symbols from left to right each represents the connection method of one and two windings, and the number indicates the connection group number of two windings. General high-voltage transformers are basically Yn, Y,d11 wiring.

In the transformer connection group “Yn” means that the primary side is star with neutral wiring, Y means star, n means with neutral; “d” means that the secondary side is triangle wiring. “11” means that the transformer secondary side line voltage Uab lags behind the primary side line voltage UAB330 degrees (or 30 degrees ahead).

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What is the number of phases and frequency?

Three-phase starts with S and single-phase starts with D. The national standard frequency f in China is 50Hz. 60Hz is available in foreign countries (e.g. USA).

What is temperature rise and cooling?

The difference between the Coal Mine Transformer winding or upper oil temperature and the transformer ambient temperature is called the temperature rise of the winding or upper oil surface. There are various cooling methods: oil-immersed self-cooling, forced air-cooling, water-cooling, tube-type, sheet-type, etc. The temperature rise of oil-immersed transformer windings is limited to 65K, and the temperature rise of oil surface is 55K.

What is the insulation level?

There are insulation level standards. For example, the insulation level of a transformer with a rated voltage of 35kV and a rated voltage of 10kV is LI200AC85/LI75AC35, where LI200 means that the transformer has a high voltage lightning surge withstand voltage of 200kV and a frequency withstand voltage of 85kV, and a low voltage lightning surge withstand voltage of 75kV and a frequency withstand voltage of 35kV. Withstand voltage is 35kV.

The current insulation level of oil-immersed transformer products is LI75AC35, which means that the transformer’s high-voltage lightning surge withstand voltage is 75kV, and the frequency withstand voltage is 35kV, because the low-voltage is 400V, which can be disregarded.

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What is the coupling group marking?

According to the Coal Mine Transformer a.. According to the phase relationship of the secondary winding, the transformer winding is connected into various combinations, which is called the connection group of the winding.

In order to distinguish the different connection group, often use the clock method, that is, the high-voltage side of the line voltage as the long needle of the clock, fixed on 12, the low-voltage side of the line voltage as the short needle of the clock, look at the short needle pointed at which a number, as the connection group of the mark.

For example, Dyn11 means that the primary winding is a (triangle) connection, and the secondary winding is a (star) connection with a central point, and the group number is (11) point.


Of course, there is a lot of content on the name plate of transformer, such as: transformer manufacturer, transformer oil type, secondary wiring diagram of transformer bushing current transformer, and the rated voltage and current corresponding to each gear of the switch, etc.

Under normal circumstances, from the transformer nameplate can find out most of the transformer information, read the transformer nameplate of each data expressed in the meaning of the transformer repair and maintenance work is very important.

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