Clamp meter testing motor and motor control circuit
One of the most challenging locations for current measurement is the control cabinet, especially when it uses IEC type components. The IEC type components originating from Europe are much more compact compared to the corresponding NEMA components, and the wiring may be encapsulated quite tightly. The Fluke 330 series clamp drives fan and pump loads. The motor can be controlled by an electromechanical starter or by an electronic variable speed drive. Variable speed drives are becoming increasingly common because they can save a lot of energy.
It is an ideal clamp type table for measuring the following motors and drivers:
Load size: The suction current of the motor measured by the average of three phases should not exceed the full load current rating of the motor. The conical clamp and backlighting function of the rated value table are very suitable for this measurement task. Multiply by the allowable overload coefficient '
On the other hand, motors with a load current lower than 60% of the full load current (most of which are) have lower efficiency and lower power factor.
Current balance: Current imbalance may indicate a problem with the motor winding (for example, different resistance is generated on the field winding due to an internal short circuit (generally, the imbalance should be less than 10%). (To calculate the imbalance, first calculate the average value of the three-phase readings; then find the maximum deviation from the average value and divide it by the average value.) When there is no current in one phase of the three phases, the extremely high current imbalance is single-phase imbalance. This is usually caused by a disconnected fuse.
Impulse current: A motor that is directly pressurized and started (through a mechanical starter) has an impulse current (which can reach approximately 500% on older motors and up to 1200% on energy-saving motors). If the impulse current is too high, it often causes voltage drops and annoying tripping. The "impulse current" function of the Fluke 337 clamp type meter is a unique feature designed to trigger and capture its true value on the impulse current.
Peak load (shock load): Some motors can withstand shock loads, which can cause sufficient current surges to trip the overload circuit in the motor controller.
Imagine encountering a hardened chainsaw during operation. The minimum/maximum function can be used to record the worst case current absorbed by the impact load.
Whether in residential or commercial facilities, clamp watches are an indispensable tool for electricians.
