Transient Limitation

Our published data provide information on maximum peak current and RMS current. Typically there is a large difference between the two. This suggests that the peak current could be observed only for very short periods of time before overheating would set in. Fortunately for unipolar pulses overheating is not a problem because saturation limits the secondary current before overheating can take place.

For bi-directional signals, such as AC waves, overheating may be a problem. However for frequencies below 60Hz ,saturation will again limit overheating. For higher frequencies, on the other hand, the Ipeak/f value of the applied signal can become smaller than the listed AC saturation value. Under this condition, saturation no longer limits the current, and overheating can become a serious problem. In this case, it is important that the listed RMS rating of the monitor is not exceeded. If short-time operation at currents exceeding the RMS rating is necessary, it is important to limit the exposure time so that a critical (I²t)cr product is not exceeded.

This critical (I²t)cr value depends on the model selected. For example, for IPC’s CM-10-L model, the (I²t)cr value is 2.5 x 10^5 A²s. For an applied current of 1 kA, the maximum on-time would therefore be 2.5 x 10^5/10^6 = 0.25s or 250ms before serious damage could be expected. IPC would be pleased to provide (I²t)cr values for different models if one wishes to use a monitor above its rated RMS current level.