Residual Current is a critical condition impacting hospitals, data centres, industrial plants, etc. It can lead to dangerous situations for both personnel and equipment.
Moreover, it can cause unexpected interruptions, malfunctions and EMC problems that cost time and money. Hence, Residual Current Monitoring is critical for safety, high availability and productivity in industrial and purpose-built environments.
Inside environments like data centres where shielded cables are present, residual current may spread through cable shielding across different parts of the data centre if the racks are insufficiently earthed. This can lead to fires, unexplained IT systems failures, tripping and disconnecting of critical equipment.
Let’s understand RCM, its dangers and the solutions a little better.
WHAT IS RESIDUAL CURRENT?
Residual Current is electrical current that occurs in an unwanted conductive path. It flows from either AC or DC circuit in equipment to the chassis, or to the ground.
Residual currents are typically the result of insulation faults, defective equipment and components (power supplies, electrical loads) causing outflow-related residual currents and stray currents in TN-S systems. RCM classification is based on frequency and waveform of the current that they candetect - Type A, Type B, Type B+.
WHY USE RCM (EARTH LEAKAGE MONITORING)?
RCM is essential to ensure Continuous System Availability. In market segments with sensitive applications (e.g., Critical power locations, Hospitals, Industrial Manufacturing), an uninterrupted power system is of crucial importance.
Uninterrupted operation (Increased Uptime & Availability) of an installation is only ensured by continuous monitoring.Continuous Residual Current Monitoring is the only method to detect dangerous fault currents at an early stage.
Early detection of insulation faults, as well as preventive maintenance and servicing outside of operating hours, can prevent unexpected shutdowns of machines, servers and systems, thus avoiding unwanted interruptions in operation, property damage and high costs.
RCM measurement in accordance with DIN EN 62020 offers the most reliable and safe alternative wherever the realization of Insulation Resistance Measurement or RCDs are not practical in an installation.
PROBLEMS CAUSED BY FAULT CURRENTS
While electricity has become an indispensable component of our lives, the fact is, it comes with its own hazards to human life and property. The major risks include:
REASONS FOR INSULATION FAILURE
The purpose of insulation is to prevent the flow of electric current between points of different potential in an electrical system. Failure of insulation is one of the most common failures in an electrical equipment.
Insulation of an electrical circuit becomes weak due to various causes:
HOW RCM WORKS
Residual currents are typically the result of insulation faults, defective equipment and components (power supplies, electrical loads).
Conductors (L1, L2, L3, N) of the specific measurement point are monitored and passed through the RCM CT. In a fault-free system the sum of all currents is ZERO, so that in the current transformer no current is induced.
If a fault current is flowing, the current difference induces in the differential CT an mA current that is detected by Janitza’s UMG device.
TYPES OF RCM
There are 3 types of RCM:
Type A: Sinusoidal alternating current pulsed direct current. This type of RCM is applied to single-phase electronic devices with electronic regulation & control such as power supplies, computers, lighting systems, single-phase drives, heat pumps, single-phase dimmers, single-phase electronic devices in the three-phase network, etc.
Type B: Smooth & pulsating direct current as well as alternating currents up to 2 kHz. Applications include devices with three-phase bridge circuits and purely direct current devices like photovoltaic systems, controlled three-phase motors, UPS systems, dimmers, medical devices, etc.
Type B+: Smooth & pulsating direct current as well as alternating currents upto 20 kHz.
RCMs monitor residual currents in electrical installations in real time. They report the level of residual current value and signal when it exceeds a threshold. They comply with DIN EN 62020.
IEC 62020 is a standard used to test RCM accuracy. It defines residual operating current IΔN as the leakage current threshold where the RCM reports an alarm.
Where a circuit is permanently monitored by an RCM in accordance with IEC 62020 or an IMD in accordance with IEC 61557-8, it is not necessary to measure the insulation resistance if the functioning of the IMD or RCM is correct.
When RCM (Earth Leakage Monitoring) is installed and operational, there is “NO” requirement for Mains Power disconnection.
WHERE IS RCM USED?
There are many applications of residual current monitors; they include:
ALTERNATIVES FOR RESIDUAL CURRENT MONITORING
Insulation Testing as part of Preventive Maintenance
Both the ends of the cable need to be disconnected and then meggered for finding the insulation. Long testing times results in long shutdown times and personnel have to deal with the cumbersome procedure of disconnecting the terminated cables. Periodicity of the tests needs long term planning as well.
Insulation Monitors - Online
This is a popular but cost prohibitive measuring method wherein a measuring DC voltage is superimposed between the phase and PE conductor. This measurement procedure is suitable for monitoring conventional AC, 3(N)AC systems. If it is used in AC, 3(N)AC systems containing galvanically connected DC components, these DC currents will distort the measurement result.
Residual Current Breakers / Earth Leakage Relays
These devices trip the circuit causing incidents. Faults and fires are not predicted, only prevented, and surprise shutdowns can be extremely expensive for operations that require uninterrupted power supply.
RCM WITH JANITZA
Janitza offers a wide range of digital energy meters that provide residual current monitoring in conjunction with energy measurement, which constitute a measure for fire protection and maintenance prevention. Downtimes and the associated costs are thereby reduced.
Timely and preventative maintenance – facilitated through the information additionally gained from an RCM measuring device – also significantly enhances the efficiency and availability of a system.
Janitza's range of smart RCM devices covers the complete electrical system from utility incomer to the final circuit:
1. MV & LV supply (PCC)
2. LV Main Distribution Switchboard
3. Sub-distribution Switchboards, UPS Outputs
4. PDU, Critical Power Supply Points & Busway Feed Box
5. Outgoing Circuits, Final Sub-measurements & Busway Tap-offs
Type A RCM measuring devices such as the UMG 96RM-E, UMG 509-PRO, UMG 512-PRO, UMG 20CM from Janitza are suitable for monitoring alternating currents, pulsing DC currents per IEC/TR 60755 (2008-01) and can be used for continuously checking for residual currents in TN-S systems.
Other Type A RCM devices include UMG 96 RM-PN, UMG 96 PA, UMG 806, RCM 201-ROGO, RCM 202 AB.
Type B RCM devices include UMG 96 RM-E, UMG 96 PA, UMG PQ-L, RCM 202 AB. The last three devices are also capable of Type B+ RCM.
Software & Apps:
Janitza's power grid monitoring software, GridVis generates the RCM report which allows clear and uncomplicated display of measurement data from residual current measurements. The GridVis RCM Report enables users to:
Janitza's RCM analysis App is a homepage add-on application with extensive options for setting limit values and for detailed analysis of residual currents. Up to 20 RCM channels can be managed and evaluated via a gateway*. The evaluation includes all types of residual currents and an associated frequency analysis.
For example, 50 Hz, pure DC or high-frequency residual currents in the 20 kHz range can be displayed individually. In addition, the application enables the proven dynamic limit value formation with Janitza energy measuring devices.
Energy measuring devices can be assigned to each of the 20 RCM channels and limit values can be calculated as a function of power.
Highly automated production systems, computer centres and systems with constant processes (e.g. food sector, cable fabrication, paper production) require a reliable power supply - often even high availability, i.e. an availability of at least 99.9%, frequently even 99.9999 %.
An insulation measurement is required for the repeat testing of fixed electrical systems for which the system must be switched off. Production processes and administration processes are interrupted. This means an increase in work and often also significant costs.
In order to avoid this, the standards offer an alternative: Continuous residual current monitoring, with which it is also possible to locate faults faster. With continuous RCM, it is possible to avoid shut-downs and minimise test work. Constant checking of the system takes place, which enables the immediate detection of faults.
With Janitza’s range of solutions for energy monitoring and management system, comprehensive RCM of the power supply takes place at all levels: from CGP and outputs requiring monitoring in the LVDS and sub-distribution systems, right through to individual critical loads. Together with the GridVis® energy data acquisition software and the integrated alarm management, users can avoid expensive downtimes and prevent fire hazards that are latent due to creeping insulation faults.
In India, Janitza products are brought to you by Messung Electrical Engineering division. Power quality analysers, digital energy meters, active filters, visualisation software and apps – Messung offers the complete Janitza range of power quality and energy management solutions.
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