BENDER RCMA475LY Residual Current Monitoring

Type B characteristics and operating conditions

RCMA475LY complies with the Type B requirements of IEC 60755 Amendment 2 and is capable of responding to various waveform residual currents. According to the operating conditions, the tripping current range is as follows: 0.5... 1 × I Δ n when the AC residual current is 50 Hz; Pulse DC residual current, including positive and negative half waves, with a half wave current of 0.5... 1.4 × I Δ n; Phase controlled half wave current, current delay angle of 90 ° el... 135 ° el, 0.5... 1.4 × I Δ n; When half wave current is superimposed with 6 mA smooth DC, it is 0.5... 1.4 × I Δ n; The smooth DC residual current is 0.5... 2 × I Δ n. These features enable RCMA475LY to cover complex scenarios such as frequency converter output side, DC power supply, UPS battery circuit, charging device, etc.

In industrial sites, six pulse rectifiers, single-phase rectifiers with smoothing capacitors, inverters, battery chargers, construction site variable frequency drive equipment, etc., may all generate smooth DC or pulsed DC residual current. If an AC type monitor is used, the DC component may cause transformer saturation or measurement deviation, resulting in failure. The AC/DC sensitive design of RCMA475LY can effectively identify these waveforms and improve protection coverage. Its typical applications include grounded two, three, and four conductor systems, single conductor monitoring without charge under normal conditions, such as N and PE conductors, as well as variable speed drive and UPS systems.

Wiring, installation, and precautions

The wiring terminals of RCMA475LY include power supply A1, A2, external measuring instruments M+, M -, external TEST/RESET terminals T/R, alarm relay terminals 11, 12, 14, and pre alarm relay terminals 21, 22, 24. The power supply voltage should be selected according to the order information, and it is recommended to use a 6A fuse for line protection. External measuring instruments can be connected to 0... 100% display heads, and the measurement converter 9604-4241 in the attachment can provide 96 × 96 mm display. RK170 can also be used to convert 0... 400 μ A input to 0... 10 V or 0/4... 20 mA output.

During installation, the phase and N wires of the monitored circuit should pass through the internal measuring current transformer. Never pass PE conductors through measuring current transformers. If the PE line passes through the transformer, some of the residual current will return through the PE line, causing the measured value to cancel or misjudge. For single-phase circuits, L and N should pass through in the same direction; For three-phase circuits, L1, L2, L3, and N should all pass through. If only monitoring non electrified conductors, such as N or PE, the system structure and monitoring targets need to be confirmed. The equipment can be installed with screws, compact in size, and suitable for installation in distribution cabinets. The transparent cover can be sealed to prevent parameters from being mistakenly adjusted.

Front panel settings and DIP switches

On the left side of the front panel are the TEST/RESET button, Power ON, and Alarm LEDs. The LED bar chart in the middle displays scales such as 10%, 50%, and 100%. There are two potentiometers on the right: one is used to set the response delay within the range of 0... 10 s; the other is used to set the response value, which, in conjunction with DIP switches, achieves a magnification of x1... x10 mA. DIP switches are used to configure key parameters:

Switch 7: Action point of pre alarm contacts 21-22-24. Position A is 50% of I Δ n1, and position B is 100% of I Δ n1.

Switch 8: Pre alarm response delay. Delay at position A is 1 second, and delay at position B is 0 seconds.

Switch 9: Operation mode of alarm relay. Position A is normally open N/O, and position B is normally closed N/C.

Switch 10: Response range. The A position is 30 mA, and the B position is 50 mA.

Switch 11: Response delay multiplier. Position A is the set value x10, and position B is the set value x1.

When setting up, the required response value of the system should be determined first. For example, if a 300 mA alarm is required, the response range can be set to 30 mA or 50 mA, and the target value can be obtained by combining a potentiometer and a multiplier switch. The response delay should be adjusted according to the load start-up characteristics to avoid false alarms caused by motor start-up and power on of the frequency converter. It is recommended to set the pre alarm threshold to 50% in order to receive alerts during the early stages of insulation degradation. If there is strong interference on site, the delay time can be appropriately increased.

Typical application scenarios

RCMA475LY is suitable for various grounding systems. In a variable frequency drive system, there are high-frequency switches and DC components on the output side of the frequency converter, and ordinary residual current monitors may malfunction or refuse to operate. The 0... 700 Hz response range and Type B characteristics of RCMA475LY can cover this type of waveform. In the UPS system, the battery circuit may generate smooth DC residual current, and RCMA475LY can monitor the insulation status of the battery to ground. In battery chargers and rectifiers, DC side fault currents may persist, making AC/DC sensitive monitoring particularly important. At construction sites, construction equipment controlled by frequency conversion, temporary distribution boxes, handheld electric tools, etc. may generate complex residual currents, and RCMA475LY can provide reliable warnings.