АНГ 2 Relay protection / Individual_Task2

1. What for the instrument transformers are used?

2. What are step-up and step-down transformers? What type of transformer are the current transformer and the voltage transformer?

3. What are primary and secondary currents?

4. What is current transformer ratio?

5. What value of ratio for distribution transformer?

6. What value of ratio for transformer inside industrial facility?

7. How can we measure the current in the circuit fed from the outlet?

1. Measuring transformers are used to measure and control (for example, in systems of relay protection of networks) voltage, current or phase of an electrical signal of alternating current of industrial frequency (50 or 60 Hertz) in a controlled circuit.

They are used in cases where direct connection of the measuring device is inconvenient or impossible, for example, when measuring very high currents or voltages. It is also used to provide galvanic isolation of the primary circuit from the measuring or control circuit.

Basic function of Instrument transformers is to step down the AC System voltage and current. The voltage and current level of power system is very high. It is very difficult and costly to design the measuring instruments for measurement of such high level voltage and current. Generally measuring instruments are designed for 5 A and 110 V.

The instrument transformer is sized to have a minimal effect on the measured (primary) circuit and to minimize waveform and phase distortion of the measured signal of the primary circuit proportionally displayed in the secondary measuring circuit.

2. A step-up transformer is a transformer that converts a low-voltage, high-current AC system into a high-voltage, low-current AC system. In this type of transformer, the number of turns in the secondary winding is greater than the number of turns in the primary winding.

A step-down transformer is a transformer that converts a high primary voltage associated with a low current into a low voltage, high current. With this type of transformer, the number of turns in the primary winding is greater than the number of turns in the secondary winding.

Based on the definitions, a current transformer is a step-up transformer and a voltage transformer is a step-down transformer.

3. Primary current is the current that flows through the primary winding of the current transformer, the standard scale of rated primary currents contains values from 1 to 40000 A.

The secondary current is the current that flows through the secondary winding of the current transformer, it is usually 5 A or 1 A.

4) Что такое коэффициент трансформации тока?

The ratio of the rated primary current to the rated secondary current is the current transformation ratio.

4. It is also equal to the ratio of the number of turns of the secondary winding to the number of turns of the primary winding.

5. Distribution transformers are used in the distribution network to provide voltage transformation in the power system by lowering the voltage level at which electrical energy is distributed and used by the consumer, so the current transformation ratio, which is equal to the ratio of the number of turns of the secondary winding to the number of turns of the primary winding, is less than one, since the number The number of turns in the secondary winding is less than that of the primary.

6. The value of the coefficient for a transformer inside an industrial facility is less than one, since it is a reduced and relative number of turns in the secondary winding is less than one, since it is a reduced and relative number of turns in the secondary winding

7. In order to measure the current in a circuit powered by a socket, in no case should a device for measuring current strength, such as a multimeter, be connected directly to the socket, since there is only voltage at its contacts in the socket, and the current will appear only when a load appears, for example, some or a household appliance, and if you connect the multimeter directly to the outlet, then it will be the consumer and all the current will go through it and it will burn out, namely, its fuse. That is why it is necessary to measure the current in a circuit powered by an outlet only by including it in series in a circuit with a load.