In an Electrical Power System currents and voltages must be monitored constantly to make sure that the values remain within the required limits. This will also switch off the faulty sections from the main supply network. It is important to identify the fault and to isolate the faulty section automatically from the network because this will result in collapse of the entire electrical power system. These protection systems need to be fast and reliable in events of fault in order to avoid any large scale damage. It is important that the protection system identifies and isolates the faulty section without affecting the remaining power system. A number of protective relays are analyzed: under/over voltage time relays, definite time over-current relays, inverse time over-current relays, combined over-current and earth-fault relay, directional relay and earth-fault relays.
Experiments:
Instrument Transformers Experiments:
- Determination of the transformation ratio of a current transformer for various primary currents and investigation on the influence of the load on the transformation ratio.
- Explanation of the terms: ratio error (current error), accuracy class and rated accuracy limit factor.
- Test on the performance of the current transformer at over-current.
- Assembly of the common current transformer circuit for measurement on three-phase network.
- Measurements of the zero-phase sequence current of a three-phase system.
- Measurements on a summation current transformer.
- Demonstration of the principle of differential protection.
- Determination of the transformation ratio of a voltage transformer for various primary voltages and investigation on the influence of the load on the transformation ratio.
- Explanation of the terms: ratio error (voltage error) and accuracy class.
- Assembly of the common voltage transformer circuit for measurements in three-phase network.
- Measurement of the residual voltage in a three-phase system with a fault to ground.
- Assembly of a voltage transformer circuit in open delta connection.
- Measurement of the three conductor voltages on symmetrical and asymmetrical loads.
Protective Relays Experiments:
- Connection of an under/over voltage relay in a three-phase network and investigation on its behavior with respect to under and over-voltage.
- Determination of the resetting ratio of an under/over voltage relay.
- Measurement of the operating time of an under/over voltage relay.
- Connection of a definite time over-current relay in a three-phase network and investigation on its behavior with respect to different settings.
- Determination of the resetting ratio of a definite time over current relay.
- Connection of an inverse time over-current relay in a three-phase network and investigation on its behavior with respect to different settings.
- Measurement of the operating time of a definite time over-current relay.
- Measurement of the operating time of an inverse time over-current relay.
- Investigation on an earth-fault relay.
- Check of the operate time set.
- Demonstration of an earth-fault alarm in a three-phase network.
- Reaction to so-called transient earth faults.
- Investigation on a combined over-current and earth-fault relay behavior connected in a solid earthed three-phase network.
- Demonstration of how the external blocking Input works.
Protection of HV Line Experiments:
- Connection of an under/over voltage relay in a three-phase network and investigation on its
- Behavior with respect to under and over-voltage.
- Determination of the resetting ratio of an under/over voltage relay.
- Measurement of the operating time of an under/over voltage relay.
- Connection of a definite time over-current relay in a three-phase network and investigation on its behavior with respect to different settings.
- Determination of the resetting ratio of a definite time over current relay.
- Measurement of the operating time of a definite time over-current relay.
- Connection of an inverse time over-current relay in a three-phase network and investigation on its behavior with respect to different settings.
- Measurement of the operating time of an inverse time over-current relay.
- Investigation on an earth-fault relay.
- Check of the operate time set.
- Demonstration of an earth-fault alarm in a three-phase network.
- Reaction to so-called transient earth faults.
Protection of HV Line Experiments:
- Demonstration of the protection of a transmission line connected in a solid earthed
- Demonstration of how an earth-fault warning relay monitors the transmission line for an earth fault in a network with isolated neutral connection network, when there is a three-phase, two-phase or single-phase short-circuit.
- Demonstration of how an under/over voltage time relay monitors the protection of a load against under-and over-voltage.
