Electrical Protective Relay

Posted by MRB
Study Objective
Analysis of existing system (time current characteristics of protective devices under fault conditions)
Identify weaknesses
Engineer remedies to alleviate weakness
Recomended solutions
Verify safety (equipment rating vs fault level)
Factors Compelling Study
Operating personnel experienced recurrent spurious trips
No prominent anomalies from visual inspection of main equipment found by supervising Electrical Engineer
SEE concerned on quality of as-built (or lack of ) as - built drawing and data
What is electrical power system protection?
Electrical Protection Fundamentals
"The Silent Sentinel" of the Electrical Power System
Often regarded as an esoteric branch of electrical engineering
Objectives of Protection
Prevent Injury to personnel
- containment of energy due to an electrical fault
- I2t > excess heating
Prevent / minimise damage to equipment
Minimise interruption of power
Minimise effect of disturbance
Main requirement of protective system
It must be automatic
Selective (Discriminate)
- Co-ordination time intervals to archive discrimination
Analysis & Finding
Analysis of Protective Devices Time-Current Curvent
Power Flow Routed # 1
No prominent abnomalities in coordinatiaon of time-current between relays
Power Flow Routed # 2
No prominent abnomalities in coordinatiaon of time-current between relays
Power Flow Routed # 3
Very distinct miscoordination of relay curves between uptream 33kV and downstream 11kV
Motor Protection
Motor relay setting sub-optimal
Result of Short Circuit Calculation
Short circuit calculations verify that all circuit breakers and main apparatus can meet and withstand the maximun prospective fault level within the system, regardless of mode of operation
Available short circuit currents at various node within the system is within the relay operating range
Revise Chiller Motor Protective Relay Settings
Include test of MPR's in the schedule of mandatory test by a testing engineer at least once in two years
Include testing of LV Motor Thermal Overload Relay (Specifically motor for critical duties)
Revise 11kV Relay no. 4d setting along Power Flow Route #3
Incidental Matters for Consideration
Institute data keeping of main equipment such as Motor nameplate data and Motor Thermal overload setting
Institute Preventive Maintenance on key equipment
Display legible, verified one line drawings in substations
Institute routing Preventive Maintenance checks on support system, e.g Fire extinguishers, Auto extinguisher system etc.
Consider change of existing HALON extinguisher system to an environmentally friendly alternative