Product Overview

 

Isolation Monitoring

Isolation monitoring is a measure of protection according to DIN EN 0100 in both isolated systems and IT systems.  The isolation monitor monitors the condition of the isolation of the supply lines in a system’s L1/L2/L3/N and all electrically interconnected parts to ground (PE/PA).

The isolation monitor serves as protection against damage of electrical equipment, buildings, and people caused by faulty or defective electrical installations.  Common fields of application for the isolation monitor are in medical areas (DIN VDE 0100-710), mobile power generators (DIN VDE 0100-717) for example on fire department vehicles and technical emergency service vehicles,  or in generators for welding according to bulletin GW308.  In industrial use, the isolation monitor is installed all over, where there is a need for high reliability of the power supply, or in process critical applications and a separation or disconnection of the power source is not possible.

Residual Current Monitoring

Differential current relays, earth leakage relays, or residual current device are recognized by DIN VDE 0100 as a protective measure in TT and TN systems, and under certain circumstances are also recognized as a protective measure against a second insulation failure in IT systems.  These devices have the task of monitoring the current flow to ground and when the current flow exceeds the threshold value, it gives a notification that can be used to shutdown the device.  Compared to the popular residual current circuit breakers (RCCB), these relays have no power source contact that would allow it to disconnect power from the system.

There are two reasons why differential current relays are preferred to RCCBs:

  1. An immediate shutdown is not desirable for operational reasons.
  2. The current loads are so large, that it makes sense for separate circuit breakers to control the shutdown.

Differential current relays are equipped with a summation current transformer for detecting the fault currents.  This is connected separately at WoKa-Elektronik, so that a spatial separation between the current transducer mounted in the power section of the device, and the electronic evaluation that is built into the control part of the device, can be achieved. 

Fault currents can be caused by different reasons.  These fault currents can occur due to leakage capacitances, isolation fault to ground, or a direct ground short.

In 3-Phase systems, the capacitance leakage currents tend to play no role most of the time.  This is due to the fact that the leakage currents flow from all active conductors symmetrically to ground and act as load currents.  However, in AC systems the capacitive filter fault currents can cause the RCCBs to trip.

Residual currents that are caused by insulation failures are a result of a gradual process.  These insulation failures are often caused by penetrating moisture or conductive contamination on live conductors.  As the insulation resistance of a live conductor deteriorates slowly, the leakage current increases.  With the ability to see the current fault current value, it can allow for counter measures to be taken so that there does not have to be a shutdown of the system.

Direct ground shorts happen often due to a mechanical action.  Here the insulation value changes from high impedance to low impedance in a relatively short time.  The low impedance causes large fault currents to flow which causes the RCD or RCCB to trip and in serious cases the circuit breaker will also trip.

Current Monitoring

Current relays monitor the operating currents of individual loads to detect faults.  Undercurrent relays detect line breaks, fuse failures, load drops on electric drives, or supply disruptions.  Overcurrent relays detect overloads through connection of loads or mechanical overloads of electric drives.  Overcurrent relays are not to be used a replacement for motor protective switches or fuses.  Current relays with a small range of measurement (20mA) can be used as limit switches in measuring circuits, and can easily be used to replace gauges with instruments with limit contacts.

 

Voltage Monitoring

Voltage relays monitor the line voltage in distribution networks for undervoltage or overvoltage.  Undervoltage or overvoltage can be of importance when an uninterrupted function must be guaranteed.

Undervoltage for an example could lead to the destruction of electric motors.  When an electric motor is sourced with a voltage lower than expected, they can become thermally overloaded.

Overvoltage can destroy or damage electronic devices due to the overload.  Overvoltages are rarely found in power-supply networks that come from the power company.  However, when generators are used in isolated operation, the generator could run out of control and create an overvoltage condition. 

Frequency Monitoring

Frequency relays monitor the system for over and under frequency conditions, in order to protect electric machines from damage.  The use of frequency relays can be versatile.  For example when a generator is being used in carousels with variable speed drives, where the maximum speed is not to be exceeded.