June 9, 2018 by Cody Whisenhunt, President

Testing Low Voltage Switchgear

Methods for Testing Low Voltage Circuit Breakers

5.0   TESTING

5.1      LOW VOLTAGE CIRCUIT BREAKER TEST DATA SHEET

A Low Voltage Circuit Breaker Data Sheet should be filled out on every rebuilt circuit breaker. Test Data Sheets need to be completely filled out, and in particular circuit breaker name plate data, job number, curve specs, test results, date and technician name. If a technician has a question on the Low Voltage Circuit Data Sheet or question on how to perform a test then he should consult his/her supervisor.

5.2      MEGGER INSULATION TESTING

Megger Insulation Test – This test is required on all Low Voltage Circuit Breakers. This test is designed to insure that the breaker has adequate insulation. Test results can vary depending on weather conditions, but in most cases a test result of 100 mega ohms or higher is satisfactory for a rebuilt 480V circuit breaker. Test should be conducted from each phase to phase, phase to ground, and line to load. These test results should be recorded on the Low Voltage Circuit Breaker Data Sheet and attached to the job sheet.

5.3      CONTACT RESISTANCE TEST

Contact Resistance Test (Ductor Test) – This test is required on all low voltage circuit breakers and designed to insure that the circuit breaker has solid and equal contact surfaces on each phase. Compare resistance to adjacent poles and similar breakers. Investigate any deviations of more than twenty percent (20%).

5.4      ELECTRICALLY OPERATED BREAKERS

Electrically operated circuit breakers should be tested by means of applying voltage at the secondary disconnects and charging the circuit breaker charging motor (if stored energy mechanism), closing the circuit breaker from the secondary disconnects, and tripping the circuit breaker from the secondary disconnects. Verify operation of the Y relay. Also test any auxiliary contact circuits, under voltage devices, and bell alarms from the secondary disconnects. Test the blown fuse device on fused breakers.

5.5      HIGH CURRENT INJECTION TESTING

High Current Injection Test – This test is required on all Low Voltage Circuit Breakers. This test insures the reliability of the circuit breakers trip units. Each circuit breaker’s trip units should function within a specified time frame at a specific overload. It is customary to test a circuit breaker’s long time function at 300% of the breakers normal load rating and short time function at 150% of its overload rating. Instantaneous is determined by increasing the current level on the test set, using the run-up or pulse method, and injecting momentary current until the breaker trips. Clearing time should be within 20% of determined instantaneous setting. Determine ground fault time delay by primary current injection at 150% if applicable. Each manufacturer provides time current characteristic curves so as to determine if a circuit breaker’s trip units are operating as designed. Check the manufacturer’s curves for the specific circuit breaker being tested and record this information on the Low Voltage Circuit Breaker Data Sheet. Each circuit breaker should be tested on all functions and on all three phases.

5.6      CELL RACK-IN TEST

Rack-in Test – This test is required on all Low Voltage Circuit Breakers. This test insures the ability of the circuit breakers to be installed into the switchgear they were designed for. This test also insures the operability of all safety interlocks. The circuit breaker will be racked into the cubicle and various tests performed at each step in the racking process. Various factory tools and rails are also tested for compatibility.

 

5.7      QC INSPECTION

Initial and date the Process Control Form. Get inspector to initial and date the Process Control Form for testing.

BCS Switchgear is an industry leader in new and obsolete electrical control and distribution equipment. Since 1997, BCS has been servicing customers to extend electrical life of low and medium voltage electrical power equipment.

Cody can be reached by email: cody@bcsswitchgear.com

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