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Widely used in substations of different voltage levels
- Sep 01, 2017 -

Power transformers are important electrical equipment in power systems, which are widely used in substations of different voltage levels. Power transformers are continuous operation of the stationary equipment, relative to the transmission lines and generators, although the operation is more reliable, less chance of failure, but most of the transformer installed in the outdoors, subject to natural conditions, but also by the connection load and power System failure, especially the modern power system, more and more use of large-capacity power transformers, high voltage level, costly, complex structure, if damaged due to failure, will cause great economic losses. In addition, the transformer failure not only affect the reliability of power supply, power system stability is also a great disturbance, the impact of a large range.

1, the transformer common faults and abnormalities

Transformer faults can be divided into internal faults and external faults.

Internal failure refers to the failure of the main body is a transformer tank failure, it includes the winding between the phase short circuit, winding or lead single-phase short-circuit and winding short-circuit between the winding, as well as for various reasons in the transformer oil Of the intermittent arc or local overheating, in the development process may also cause a variety of failures.

External failure refers to the fuel tank outside the lead of a variety of phase short circuit or single-phase ground short circuit. Transformer failure, especially the internal fault arc, will not only damage the winding insulation, burn the iron core, but also may produce a large number of vaporization gas, causing the tank explosion. Therefore, when the transformer fails, the protection device should quickly remove the faulty transformer.

Principle of transformer protection configuration

(1) Gas protection: Gas protection is used to reflect and eliminate various short circuit and oil level inside the transformer tank. For 0.4MVA and above workshop oil-immersed transformers and 0.8MVA and above oil-immersed transformers, should be installed gas protection. With load regulator transformer oil pressure regulator switch, should also be installed gas protection.

(2) longitudinal differential protection or current quick-break protection: longitudinal differential protection or current quick-break protection as transformer internal, casing and lead wire short-circuit fault main protection. For the voltage of 10kV and below, the capacity of 10MVA and below the transformer using current quick-break protection. Voltage above 10kV, the capacity of 10MVA and above transformers using longitudinal differential protection. For 10kV important transformers, longitudinal differential protection can also be used. The voltage of 220kV and above transformers using digital protection, should be used dual protection configuration (except for non-power protection).

(3) phase short circuit backup protection: reflect the external phase short circuit caused by transformer over-current, and as a gas protection and longitudinal differential protection reserve, 35kV ~ 66kV and below the small capacity step-down transformer should adopt over-current protection, 110kV ~ 500kV drop Pressure, boost and system contact transformer should adopt the composite voltage to start the over-current protection or composite current protection.

(4) ground short-circuit backup protection: 110kV and above the neutral point of direct grounding in the various transformers, when the transformer neutral point may be grounded or not ground operation, to reflect the external single-phase ground short circuit caused by over-current, and Due to loss of grounding caused by the neutral point of the neutral transformer, should be installed with the corresponding zero sequence overcurrent protection and zero sequence overvoltage protection.

(5) Overload protection: should be installed to reflect the winding side of the transformer over load overload protection

(6) over-excitation protection: for the high-voltage side of the 330kV and above the voltage level of the transformer, should be installed over-excitation protection. (7) Other protection: should be installed to reflect the transformer oil temperature, winding temperature and pressure inside the tank, or cooling system failure protection.