FAT Procedure for Low Voltage (LV) Switchboard

The Factory Acceptance Test (FAT) procedure for Low Voltage (LV) switchboards entails checking the design and functionality prior to installation. 

Inspections, functional testing of components & systems, and assuring specification and standard compliance are all part of the process. This procedure assures that the switchboards meet performance & safety standards prior to installation.

Purpose

The purpose of this post is to define the FAT (Factory Acceptance Test) procedure for the Low Voltage Main Switchboard.

1. Visual Inspection Test 
2. Insulation Test 
3. High Voltage Injection Test 
4. Primary Current Injection Test 
5. Metering Current Transformer Polarity Test
6. Secondary Current Injection Test 

Working Location

The authorized LV main switchboard will be used for the FAT.

Equipment to be Used

• Digital insulation Continuity Tester 
• High Voltage / Flash Tester 
• Primary Current Injection Test Set 
• Secondary Current Injection Test Set
• Elcometer Thickness Gauge 
• Torque Wrench 
• Dial Caliper Range (0-150mm)

FAT Procedure

Visual Inspection Test

• Check fitting component layout.
• Check switchboard dimensions, busbar and cable sizes, earthing conductors, and feeder entry point placement.
• Verify the brand, model, and circuit identification of installed components, including breakers, fuses, current transformers, voltmeters,  ammeters, power meters, and protection relays.
• Inspect paint work, door locking mechanism, gasket, hinges, and cut-out holes.
• Check busbar & cable tightening, markings, clearance, base angle bar, and plinth.
• Check the labels, nameplate, and phase identification.

Insulation Test

Perform a 500V megger test for 

• Phase to Earth, 
• Neutral to Earth, 
• Phase to Neutral, and 
• Phase to Phase 

to determine insulation resistance with all breakers in the ‘ON’ position.

High Voltage Injection Test

• Perform a 500V megger test between each stressed phase & all other phases connected to exposed conductive elements, with all breakers in the ‘ON’ state.
• Apply 2.5kV AC voltage to each strained phase and any other phases connected to exposed conductive elements for 60 seconds, then measure the leakage current.

Primary Current Injection Test

• Temporarily short the R, Y, B, and N primary bars on one side of the protective current transformers.
• Connect the primary injection test set to R-phase and N to primary bars on other side of current transformers.
• Connect an ammeter to CT’s R-phase to monitor the secondary current.
• To monitor the spill current, connect a milliamp meter to earth-fault relay current coil.
• Inject 50% & 100% of CT ratio via the primary bars, and record the spill current. At the same time, record the R-phase’s secondary current.
• Repeat the above-mentioned test with both Y and B phases.

Secondary Current Injection Test

• Set the current plug setting of the IDMTL relay to 5A rated current and 0.1 TMS for the 3/10 characteristic.
• Inject 5A of secondary current into R-phase, then adjust the pickup current to 5A.
• Inject 10A, 15A, and 25A into R-phase & record the tripping time, correspondingly. The time should be between +30% & -10% of the normal timing.
• Choose the intended current setting and then modify the pickup current appropriately.
• Repeat the test using Y and B phases.

Metering Current Transformer Polarity Test

• Temporarily short the R, Y, B, and N primary bars on one side of protective current transformers.
• Connect the primary injection test set to the R-phase and Y-phase primary bars on the opposite side of metering current transformers.
• Connect an ammeter to CT’s R-phase to monitor the secondary current.
• To monitor the leakage of current, connect a milliamp meter to the earth line.
• Inject 50% & 100% of CT ratio via the primary bars, and measure the spill current accordingly. At the same time, record the secondary current in the R-phase.
• Repeat the test described using Y-phase by connecting the principal injection test set on Y-phase & B-phase.
• Repeat the test indicated using B-phase, linking the principal injection test set on B-phase & R-phase.

Safety & Risk Control

• To control the hazards during the FAT, the following arrangements will be made.
• Safety barriers will be constructed around the area where the FAT will take place.
• Danger signs will be hung to warn those who approaches the FAT region.
• The RED color warning lamp will be made to flash while delivering electricity to the board for testing.
• Fire extinguishers will be positioned for emergency use at the FAT area.
• A first aid kit will be placed in the FAT area for the emergency purposes.