Useful Functions and Precautions for Using L-Load/C-Load in PCR-LE Series

Posted on: June 23rd, 2021 by Doug Lovell

1. When Using Inductive Load (L-Load)1-1 Soft Start

A typical L-load is a motor load. E.g.) If using an induction motor load, the startup current can be 5 times (or more) larger than the normal startup current and it flows for several hundred ms.
In this situation; 1) The motor load becomes inductive. 2) The power factor is approx. 0.5 at peak current.
PCR-LE Series features the Soft Start function to gradually increase the startup voltage when OUTPUT is turned on. If Soft Start is set to ON in the above situation; 1) The startup current (peak current) decreases. 2) The power factor is approx. 0.65 at peak current. 3) The startup voltage gradually rises for up to 3 seconds.

1-2 Output Capacity Reduction Due To Power Factor

As described in the above, the power factor decreases and the higher current flows for several hundred ms with the motor load. Since this period is quite short, it can be considered as the instantaneous peak current. The instantaneous peak current ratio decreases due to the power factor (see the table below).

2. When Using Capacitive Load (C-Load)
2-1 Soft Start
PCR-LE Series supports the DC output mode. In DC mode, the peak current in C-load changes with the voltage rise slope and can be calculated as: I=LdV/dt. Since the voltage rise time of PCR-LE Series is from 15μs to 70μs, the high peak current may flow depending on the capacitor size. To prevent it, turn Soft Start on to decrease the peak current.
2-2 Surge Suppression Function
Generally, if the output is suddenly interrupted, the L-load releases energy. It means that;
1) It becomes the high impedance state due to the sudden interruption. 2) The L-load generates the surge voltage and it is biased to the power supply as overvoltage.
To prevent it, PCR-LE Series features the Surge Suppression function. When OUTPUT is turned off while Surge Suppression is set to ON (factory default setting), the output voltage stays at 0V for approx. 200μs and then the output impedance becomes high.
For C-load or capacitive DUT:
Surge Suppression is ON: If OUTPUT is turned off in DC mode, the output voltage rapidly falls (see Fig. 3) and the current flows from DUT to PCR-LE Series.
Surge Suppression is OFF: See Fig.4. This is equivalent to having the interruption due to wiring disconnection. It may meet the requirements of IEC6100-4-29 (interruption in high impedance state).

2-3 Response Speed

PCR-LE Series uses a high-speed linear amplifier to provide high-quality/high-stability output. It can freely control the broadband waveform; however the output may become unstable depending on the capacitive load capacity or wiring conditions. To improve it, you can set the response speed of the internal amplifier to SLOW.
Response speed mode for PCR-LE Series:
Rated power capacity is 4kVA or less: FAST, MEDIUM, SLOW Rated power capacity is 6kVA or more: MEDIUM, SLOW

Products Mentioned In This Article:

PCR-LE Series please see HERE