Short-circuit voltage: It is the voltage of the rated frequency applied to generate the rated current in another coil (at the rated tap position) when one coil is short-circuited, expressed as a percentage of the rated voltage, which reflects the transformer impedance (resistance and leakage impedance) parameters, also known as the impedance voltage (temperature 70 °C).

Short circuit: In a three-phase circuit, a small impedance or direct connection between phase and phase and phase to ground causes a sharp increase in current in the circuit, a phenomenon called a short circuit.

Short-circuit loss: It is the power absorbed by the transformer when the rated current of the rated frequency passes through one coil of the transformer, and the other coil is short-circuited, which is the loss generated by the resistance of the transformer coil, that is, the copper loss (the coil is at the rated tap point position, the temperature is 70 °C).

Short-term load: only 10-120min load each time.

Intermittent load: work repeatedly and periodically, and its load does not exceed 10min per cycle.

Secondary circuit: A circuit formed by secondary equipment in a certain order, which is called a secondary circuit or secondary circuit.

Secondary equipment: Secondary equipment is auxiliary equipment for monitoring and measuring, operation control and protection of the work of primary equipment, such as instruments, relays, control cables, control and signal equipment, etc.

Generator auxiliary protection: generator relay protection to supplement the main protection, backup protection and abnormal operation protection performance and increase the protection "such as the voltage inductor circuit may be broken, the circuit breaker may fail or flashover, the generator in the starting, synchronization, shutdown process may occur accidents, etc., these main protection and backup protection can not be detected, so add more auxiliary protection to the large unit as a supplement.

Generator backup protection: In generator relay protection, when the main protection is out of operation or fails and refuses, it can still respond to the fault and act on the relay protection of the relevant circuit breaker and automatic device. It mainly includes composite current quick break protection, impedance protection, and overcurrent protection in the direction of compound voltage starting.

Generator Efficiency: The ratio of generator output power to drilling power expressed as a percentage. Unless otherwise specified, it refers to the value at the rated operating condition.

Lightning protection grounding: It is a grounding set up for the needs of lightning protection. For example, the grounding of lightning rods (wires) and lightning arresters is to make the lightning current smoothly introduced to the earth, so as to help reduce the lightning overvoltage, so it is also called overvoltage protection grounding.

Split transformer: A multi-winding power transformer consisting of one high-voltage winding per phase and two or more low-voltage windings with the same voltage and capacity. The normal power transfer of a split transformer is only carried out between the high and low voltage windings. In the event of a fault, it has the effect of limiting the short-circuit current. The low-voltage winding of a split transformer is also called a split winding.

Induced electromotive force: The electromotive force that is generated in the magnetic flux that passes through the area around which the conductive loop changes, or at both ends of the wire when the wire cuts the magnetic field lines.

High-voltage circuit breaker: also known as high-voltage switch. It can not only cut off or close the no-load current and load current in the high-voltage circuit, but also cut off the short-circuit current through the action of relay protection device when the system fails. It has a fairly complete arc extinguishing structure and sufficient breaking capacity.

Disconnector: a kind of switchgear that has a specified insulation distance and visible fracture between the contacts in the opening position, and can bear the normal working current and short-circuit current in the closing position. When the working current is small or the voltage between the two terminals of the disconnector does not change before and after closing and breaking, the disconnector has the ability to close and break the circuit, and has both operation and isolation functions.

Working grounding: In order to ensure the safe and reliable operation of electrical equipment in normal or fault conditions and prevent high voltage caused by equipment failure, it must be grounded at a certain point in the power system, which is called working grounding.

Power factor: the ratio of the active power P to the apparent power S.

Back-up protection: When the main protection does not operate or the circuit breaker refuses, it is used to remove the fault protection.

Transformer is a sensor that obtains electrical primary circuit information from secondary equipment such as measuring instruments, relay protection and automatic devices in the power system. The function of the transformer is to turn high voltage and high current into low voltage and low current in proportion.

Breakdown voltage: When the insulating medium breaks down, the voltage applied to both ends of the medium is called the breakdown voltage.

Relay starting current: The small current value that can make the relay operate.

Contactor: It is a low-voltage switch used to turn on or off the load current in the circuit at a long distance, and is widely used in the circuit of frequently starting and controlling the motor.

Ground resistance: refers to the resistance encountered when the current enters the ground through the grounding body and spreads around.

Regular load: the motor should be used in continuous operation every day;

Distance protection: a protective device that reflects the distance from the fault point to the protection installation.

No-load current: When the transformer is running at no-load, the main magnetic flux is established by the no-load current, so the no-load current is the excitation current. The rated no-load current is the three-phase arithmetic average of the current drawn by the transformer when the positive and weak AC rated voltage of the rated frequency is applied to one coil (at the rated tap position), and the rest of the coils are open circuits, expressed as a percentage of the rated current.

No-load loss: It is the power absorbed by the transformer when the sinusoidal AC rated voltage of the rated frequency is applied to one coil of the transformer (at the rated tap position), and the rest of the coils are open, which is used to supply the core loss (eddy current and hysteresis loss) of the transformer.

Fast relay: Generally refers to a relay with a relay action time of less than 10 milliseconds.

Exciter term value voltage multiple: the ratio of the DC voltage value that the exciter of the synchronous generator can provide under the rated speed and specified conditions to its rated excitation voltage.