Protection for a high voltage motor
CASE STUDY - PROTECTION FOR A HIGH VOLTAGE MOTOR
CASE STUDY: PROTECTION FOR A HIGH VOLTAGE MOTOR
Replacement of obsolete discrete protection relays with a multifunctional digital relay to protect a 1100kW 6.6kV motor.
Scope of works
- Engineering, procurement and installation of a protection relay for a 1100kW HV motor
- Carry out relay programming and coordination study
- Refurbishment of the low voltage control compartment of the HV feeder panel
- Prepare schematics and loop diagrams
- Testing and commissioning
- As-built drawings and documentation
Considerations
High voltage motor protection requires a correctly programmed multifunctional digital relay.
Programmed settings include earth faults and thermal protection of the motor windings both for overload current and against stalling due to damage to, or seizure of, the driven machine. Thermal protection settings need to be matched to the motor’s hot and cold withstand time characteristics. Further, protection is required against harmonics or unbalanced supply loads such as single phasing which lead to negative sequence currents and rapid overheating of the motor windings. Excessive starting time or too frequent starting attempts can also damage the motor. For larger motors, winding differential protection and vibration monitoring system interfacing is needed. Excessive starting time or too frequent starting attempts can also damage the motor. Under-current protection against abnormal conditions in the driven machine is often desirable; for example, the loss of fluid feed which can lead to cavitation and severe damage to a pump.
Implementation
All these requirements were matched to the manufacturer’s test data and factored into the programming of the new relay which was installed in the refurbished low-voltage compartment of the high-voltage feeder panel. Documentation was prepared including a comprehensive coordination study and a set of protection curves.
Similar coordination and protection studies can be carried out using either proprietary software for larger systems or manual calculations for small stand-alone installations. For further details contact This email address is being protected from spambots. You need JavaScript enabled to view it.
