The multipurpose filter provides extremely good measurement accuracy and excellent noise rejection. It is capable to extract magnitude, phase angle and specific frequency of any signal (e.g. 37,2Hz) present in the waveforms of the connected CTs and/or VTs. For example, the magnitude and phase angle of the required phasor can be estimated even if it has magnitude of one per mille (i.e. 1‰) in comparison to the dominant signal, often being the power system fundamental frequency itself. When this filter is used in conjunction with REG670’s multi-purpose protection function, overcurrent function, overvoltage function or over-power function, many different protection applications can be arranged. One such example is the sub-synchronous resonance protection for turbo generators.
New features released in generator protection, Relion® REG670, version 2.0
Several new features and functions are now available in the new version of Relion® REG670.
Sub-synchronous resonance protection, based on the multipurpose filter
Generator rotor overload protection
The generator rotor overload function protects the rotor winding against excessive heating due to a prolonged overcurrent condition. The function’s operating characteristic is designed in accordance with the American standard IEEE-C50.13. For static exciters, the function uses the rotor winding’s DC current for its operation. The rotor winding’s DC current can be calculated from the AC currents measured on either the high voltage side (HV) or the low voltage side (LV) side of the excitation transformer. For HV side measurement, ratings of the excitation transformer shall be given. When the rotor DC current is used, the function can provide a DC current ripple alarm, in the event of problems with the static excitation equipment. The rotor winding DC current can also be sent to the plant supervisory system via a communication channel or displayed on the IED’s built-in HMI. The function can also be used to detect under current conditions in the rotor winding; indicating either under-excitation or loss of excitation of the synchronous generator.
Generator stator overload protection
The generator stator overload protection function protects the stator winding against excessive heating due to a prolonged overcurrent condition. The function’s operating characteristic is designed in accordance with the American standard IEEE-C50.13. For its operation the function either measures the true RMS current of the stator winding or weighted sum of the positive and negative sequence components in the stator winding.
Frequency time accumulation protection
The frequency time accumulation function records and accumulates the time during which the machine and associated steam turbines operate within pre-defined frequency bands, over a long time period (e.g. years). Once the time prescribed by the turbine manufacturer is exceeded the protection will give an alarm or may even trip the machine, depending on the customer preference. Several frequency bands can be defined and monitored.
Under impedance protection for generators and transformers
The under impedance protection offers a three zone full scheme impedance protection using offset mho characteristics for detecting faults in the generator, generator step-up transformer and out into the transmission system. The three zones have fully independent measuring loops and settings. An undervoltage seal-in feature ensures tripping even if the current transformer goes into saturation during the fault. A positive sequence based load encroachment feature for the second and the third impedance zone is available. Additionally, the under impedance protection function has a built-in feature to secure accurate reach measurement through a star-delta connected step-up transformer.
Voltage restrained time overcurrent protection
The voltage restrained time overcurrent protection function can be used as generator backup protection against short-circuits. The overcurrent protection feature has a settable current level that can be used either with definite time or inverse time characteristic. Additionally, it can be voltage controlled or restrained. One separate undervoltage step with definite time characteristic is also available within the function in order to provide functionality for generator overcurrent protection with undervoltage seal-in.
VT fuse failure supervision based on voltage difference
The VT fuse failure supervision function continuously compares the voltage level among two three-phase VT circuits. It detects single-, two- or three-phase fuse failure very quickly in order to prevent unwanted operation of any high speed protection function (e.g. distance or under-impedance protection)
The pulse integrator function provides integration of pulsating binary signals (e.g. output of the loss-of-excitation function, or out-of-step function, or reverse power function) in order to assure proper operation of the IED under different operating conditions in the power system.
New local HMI module
The REG670 version 2.0 features an improved local HMI. As previously, the HMI has a graphical display, capable of showing a user defined single line diagram and providing an interface for controlling or monitoring of the primary switchgear and on-line measurements. Five user defined command buttons are now included, enabling shortcuts into the HMI menu tree or the possibility to issue a binary command to the IED. Fifteen user programmable tri-color LEDs with three software pages are also included. They can be used to indicate the status of up to 135 binary signals to the operator.
For more information about Generator protection REG670, please refer to the Generator protection REG670/650 brochure and REG670 Product Guide.