Applications

Waveforms for Motor’s Starting Current

Logging (Recording)Waveform Graph

Companies sometimes replace motors with lower-power-consumption alternatives in order to save energy. The high levels of energy savings and cost-effectiveness promised by this approach are likely driving up the number of such replacements. (For example, this trend is particularly noticeable for 3-phase induction motors [industrial motors], which became eligible for benefits under Japan’s “top runner” program in April 2015.)

However, this approach demands a certain amount of caution, not only with regard to the motors that are used, but also to the capacity of the associated circuit breakers.

Motors that deliver high energy savings tend to have a larger starting current than conventional motors. If the circuit breaker to which such a motor is connected lacks sufficient capacity, it will trip when the motor starts.

It’s not unusual for motors to operate without incident at the time of installation, when circuit breakers have adequate capacity since other machinery is stopped, but for circuit breakers to trip once the plant is operational again. Adding capacity can be problematic since there may not be enough space in the panel to accommodate the new breakers, not to mention the additional installation costs that such changes can entail.

To avoid moving one step forward and then two steps back, it’s important to study and design your project in advance.

With GENNECT Cross, you can record starting current waveforms before and after installation.

The inrush function provided by the AC/DC Clamp Meter CM4372/CM4374 can be used to measure a motor’s starting current. The function simultaneously records RMS values and maximum crest values for motor’s starting currents. Although the clamp meter only displays numerical values, you can display waveforms for starting current as well by using the instrument in combination with GENNECT Cross.

By recording not only measured values, but also waveforms for starting current before and after motor replacement, it is possible to boost the reliability of installation work.

For example, consider a situation in which you must explain to a customer why it’s necessary not only to spend money to install new motors, but also to replace the circuit breakers. It is often difficult to obtain customers’ understanding using values alone, but showing them waveforms can be more convincing. If a customer asks for a work report, you can prepare a clear document that’s a step above in terms of quality.

*Waveform display functionality can be used for voltage as well as current waveforms.

GENNECT Cross has another function that’s useful in advance study.

You can use the app’s logging function to assess the changes in current flowing to circuit breakers over the course of a day in order to determine whether the circuit breakers’ capacity is adequate. When conducting an advance study or installing the motors, the starting current that flows to the motor won’t cause the circuit breaker to trip if other equipment doesn’t consume too much current. However, those same circuit breakers may trip when other equipment is operating—that is, when the starting current flows under conditions of high load.

To avoid this situation, you can assess current consumption under conditions of both low and high load by recording variations in current over the course of a day in advance. In this way, GENNECT Cross’s logging function can be used to log the clamp meter’s current values. By recording variations in the load current over the course of a day, you can ascertain the maximum load current to allow more reliable installation work.