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Load Bank Troubleshooting
These recommended checks are meant to guide an experienced technician through investigation of a few of the most common load bank issues. A certain level of electrical knowledge and familiarity with electrical drawings is assumed. These checks may or may not apply to your load bank. See the Load Bank Operator's Manual and Drawings Package that was provided with the unit for verification and details. If these checks do not pinpoint the problem or if more information is needed call the Simplex Service Department at 800-637-8603.
COOLING FAN MOTOR WILL NOT START/OPERATE FAN FAILURE INDICATED FAN OVERLOAD INDICATED HIGH EXHAUST TEMP INDICATED OPEN THERMOCOUPLE INDICATED HIGH INTAKE TEMP INDICATED HMI/PLC COMM ERRORS OTHER HMI ISSUES REDUCED KW OUTPUT OR PHASE IMBALANCE METER COMM ERROR INDICATED METERING ISSUES AUTOMATIC LOAD LEVELING ISSUES Cooling Fan Motor Will Not Start/Operate Check for presence of correct fan/control power. Check Fan Circuit Breaker (FCB) is closed. Check fan circuit Overload Relay (OLR). Reset if tripped. Check that Fan Motor Contactor (FMC) closes. Check that the pilot relay for the FMC closes (See drawings for details). Ensure the PLC is in Run mode (generally, Power and Run indicators on PLC are lit). Fan Failure Indicated Ensure fan is running (If not, see COOLING FAN MOTOR WILL NOT START/OPERATE). Ensure fan is turning in the correct direction. Air should be pulled in at the bottom of the unit and exhausted out the top. If fan is spinning the wrong direction, check phasing on fan power connection. Check for airway obstruction at the intake and exhaust. Check the differential pressure switch. The switch uses a length of nylon tubing to compare the pressures on each side of the cooling fan. This tube must be free of any blockage. CAUTION Blowing forcefully into the differential pressure switch may damage the switch. Never use compressed air to clear the tube. Fan Overload Indicated Ensure all sources are de-energized and locked out. Check fan for any obstruction. Ensure blade will spin. Reset the Overload Relay (OLR) located inside the control cabinet. The OLR must be manually reset. High Exhaust Temp Indicated Check for obstruction of airway intake and exhaust. Ensure that hot air is not being recirculated into the intake of the load bank. Ensure ample airflow. Verify open air clearance around load bank is within required dimensions. Open Thermocouple Indicated Check thermocouple connection for tightness at PLC thermocouple card terminals. Check thermocouple wire for any break. High Intake Temp Indicated Check ambient temp around the load bank air intake. Ensure hot exhaust from the load bank or other equipment is not being directed toward the load bank's intake. If the unit's intake temp is monitored by a button style thermal limit switch (INTS) check the switch connections and check the switch for a failure. HMI/PLC Comm Errors Check communication cable between HMI and PLC. Ensure the PLC is in Run mode. "Power" and "Run" green LEDs should be lit. Other HMI Issues Error codes prefaced with "PLC" indicate issues between the HMI and the PLC, either communication or data mismatch errors of some type. Make the checks listed in HMI/PLC COMM ERRORS and call Simplex Service for assistance. Error codes prefaced with "RTE" (Run Time Errors) generally indicate issues within the HMI operating system itself. Example 1: RTE-002 - Log Failed. (Device) cannot be found: This error will appear when the system is set up for data logging, but no USB drive is present to log data. This error will not affect load bank operation but may be a nuisance. Insert a data logging flash drive or ensure that the Start/Stop Logging button on the data logging screen is set to stop. Example 2: RTE-500 - SRAM Check Sum Error: The memory in the HMI has been corrupted, possibly by a power loss or other external event. The memory will have to be wiped and the program reinstalled. Screen is black/dark: a. Touch the screen to ensure it is not in sleep or screen saver mode. b. Ensure there is power to the HMI. c. Check for a bad backlight by shining a flashlight on the screen to see if screen elements appear. Reduced kW Ouptut or Phase Imbalance A power output of more than 5% below the rated or expected output may indicate an issue. Many factors may contribute to a reduced load bank capacity. Check system voltage: A reduced voltage input will result in a derated power output, by the formula: kW _output = kW _rated * ( V _input / V _rated )². Use manual loading or the system self-diagnostic feature to pinpoint a reduced capacity load step. The most common causes of a reduced load step capacity are: a. Blown load fuses - After pinpointing the affected step(s) refer to the unit's drawing package to identify the step's load fuses. b. Open resistive elements - See unit's drawing package to trace element connections back to their associated load contactors. Using an ohmmeter, measure each phase-to-phase resistance on the load side (output side) of the contactors. The three readings (A-B, B-C, C-A) should be balanced, meaning that all three resistance readings will be virtually identical or very close to each other, and none should read open. Note that larger steps will comprise more than one contactor, so each contactor will control a segment of the step. To find the rated resistance for the segment under measurement, use the drawings to determine the rated kW value of the segment (rated step value divided by the number of segments into which the step is divided) and refer to unit's rated resistance and current to determine the expected line to line resistance. c. Other components - A chain of control components is associated with each load step: PLC Output - Pilot Relay(s) - Load Contactor(s). Refer to the unit's drawing package to trace the controls. A failure at any of the control components could result in a missing, reduced capacity, or imbalanced load step. a. Check for accurate metering. See METER COMM ERROR INDICATED and METERING ISSUES for issues with the digital metering package. Meter Comm Error Indicated The PLC communicates with the unit's Digital Metering Package (DMP) through a serial communication connection. If the PLC fails to communicate with the meter, a Meter Comm Failure will be indicated. Check meter connection wiring per unit's drawing package. Check meter's power supply connection per unit's drawing package. Metering Issues Voltage: Displayed voltage zero, imbalanced or does not match system voltage: a. Check Metering Fuses MF 1-3. b. Check voltage connections from the bus to the metering transducer per unit's drawing package. Current / kW: a. Current Zero b. Check ground connections on CTs. Current imbalanced, low, or off, or kW low, negative, or off: a. Check CT polarity. All CTs should be installed so that the X1 / H1 side faces the source. b. Check CT connections. c. Check phasing. Voltage and Current inputs to the meter must be connected exactly as shown in the drawing package. Automatic Load Leveling Issues Automatic Load Leveling works off a kW feedback from the metering package. If the metering is not reporting kW properly, the PLC may continue adding load, looking for a user-programmed setpoint. Check for Metering Issues as above. Check Auto Load Leveling Settings.
WARNING It is sometimes necessary to have control power energized when troubleshooting in a load bank cabinet. Be aware that load banks may have multiple sources of power (test source power, fan/control power, anti-condensation heater power, etc.). Remove as much power as possible before troubleshooting. When control cabinet doors are open, treat every component and circuit as though it were live and always use all appropriate PPE.