Supervision of a grounded (3-phases+N+G / 3-phases+G / 1-phase+N+G high resistance grounded) electrical system or grounded electrical system with isolated ground

In a grounded distribution network the return current flows through the neutral conductor (N) back to the main ground bus. The current in the ground (G) conductor is theoretically zero. However, in reality there is a small current in the G conductor the so called inherent leakage current. It is caused by different devices, filters and big fluorescent lamp groups connected to the distribution network. This leakage current increases if there arise faults in the distribution network insulation damages in the devices connected in the distribution network or insulation faults in the distribution network itself. These faults may appear as partial or complete short circuits between the ground conductor and the power supply. It is important to detect the coming fault and remove it quickly in order to guarantee the appropriate operation of the grounded distribution network. A continuous fault situation may be fatal for the user, for the equipment connected to the distribution network as well as for the network itself (overheating and fire risk).

Supervision of Purity of the Electrical System

If a partial or complete short circuit between the N and G conductor occurs, a part of N-conductor current goes through G-conductor and conductive parts of building management causing fault currents. Fault currents cause potential differences and disturbance voltages (Grand Noise) in computer networks. These disturbances are especially harmful in data lines. Only by continuous supervision of a grounded network the network may be kept ”clean”.

Detection of wiring error

Wiring error may spoil the advantages of a grounded electrical system from being achieved and cause hazards for the user.
With the help of a supervision unit the wiring errors may be detected immediately. Possible wiring errors are:

• N and GND conductors are connected together,
  not only through the main ground bus.
• N and GND conductors have been swapped somewhere in the electrical system
• A load has been connected between a phase conductor and the ground
• A device is grounded through its installation parts
• Neutral to neutral wiring errors (if the measurement is close to the load)

ON-LINE prediction of insulation faults

The most usual reason for a fire risk is the damage in the cable insulation. This may occur due to overloading, excessive moisture, insulation deterioration, mechanical stress, etc. The supervision equipment detects an incipient insulation damage as the fault current value rises. The Superintend system detects an arcing fault before a fuse or a circuit breaker operates.

Supervision of the integrity of a distribution network

Leakage and stray currents cause potential differences and disturbance voltages in computer and building management networks. These power disturbances are particularly harmful in data lines. If a partial or complete short circuit occurs between the N and G conductors, the electrical system operates as a four-conductor system. In this case the benefits of a five-conductor system are lost. Only by continuous supervision of a grounded electrical system, can the system be kept “clean”.

Measurement of small currents

With this Supervision Unit it is possible to measure small currents
in the range of 1 mA to 12 A.

ON-LINE MONITORING
OF ELECTRICAL INSULATION

Over time leakage current increases because the insulation begins to degrade. By continuous monitoring of leakage current, weakened insulation can be identified before the circuit breaker trips and production is shut down.

An Example of Monitoring:

1. Monitoring unit VRE-80 2. Measuring cables 3. Sum Current Transformers 4. Recorder

DISPLAY

Main display

The main display mode provides a possibility to view the status of all supervision points and devices simultaneously.
The main display mode includes:

• Current in the supervision points relative to the set point (numbers 0 … 9)
• Short duration alarms (P)
• Over-current and equipment alarms, which are either acknowledged or not acknowledged (A and F)
• Status of the channel: connected or disconnected (.)
• Number of the channel connected to the analog output (output 1)

Channel display

Channel display shows the number (1) and name (SUB # 01) of the measuring point, measured current 96 mA.

SETTINGS

	1.	2.	3.
				1. Hysteresis 2. Time delay 3. Alarm setting

Alarm setting From 5 mA to 10 A	Alarm delay setting up to 95 secs	Name setting

ALARM DISPLAY

	Alarm display: P= alarm shorter than time delay setting A= blinking "A" - letter Red blinking LED-light
	A= blinking "A"- letter Red blinking LED-ligh

SELF TESTING

	Superintend VRE-80 tests continuously the condition of itself and the whole measuring chain. The test of the measuring chain is done at about 1 minutes intervals. If the equipment is in condition the "channel condition" display mode shows "Chann.ok!". If one measuring point has a failure, an "F" character exists in that channel.

MAX/MIN CURRENT READING

Each channel of the monitoring unit has a memory place for highest and lowest measured current. The memory is zeroed at each channel display by pressing "OK". After the measure is zeroed the current will display latest measured current.

CONNECTIONS OF VRE-80

Supply voltage and relay

The connections on top of the VRE-80: power and relay (view from the top).
In the figure the relay is in alarm state and the main unit without power.

NOTE! Relay output:

USA Other countries

120 V AC 5 A 250 V AC 5 A

INTERCONNECTION CABLES
WIRING WITH STANDARD MEASURING CABLE

Standard measuring plug-in cables:
USA			Other countries
VMP-2f VMP-6f VMP-16f VMP-32f	length length length length	2 feet 6 feet 16 feet 32 feet	VMP1 VMP2 VMP5 VMP10	length length length length	1 m 2 m 5 m 10 m

WIRING WITH INSTRUMENTATION CABLE

Installation with screw terminals

The VMPH-2F measuring cable for the current transformer is 2-feet long (0.6 m). One end of the cable has a plug connector (for the VRE-80 unit) and the other end has four colour-coded wires for connection to screw terminals on the instrumentation cable.

Installation with plug-in measuring cable

The VMP-2F measuring cable for the current transformer is also two-feet long (0.6 m). Both ends of the cable have plug connectors. The VMPA-1 (one channel model) and VMPA-4 (four channel model) are adapters for VMP-2F measuring cable. The adapter has socket(s) for VMP-2F measuring cable and screw terminal(s) for the instrumentation cable.

ANALOG OUTPUT (AC-output)

The curve corresponds the analog output voltage measured in the VRE-80.
A linear voltage output is gained when the current is below 2.5 A.

TECHNICAL SUMMARY

Leakage Current Monitor VRE-80
Supply voltage	USA 110-120 V +10% 60 Hz Other countries 230 V +10% 50 Hz
Power consumption	4.5 VA
Operating temperature	+22...+122°F (-5...+50°C)
Storage temperature	-4…+158°F (-20…+70°C)
Humidity	<95%, non condensing
Dimensions	shown on the next page
Installation
- mains and the alarm relay	screw terminal
- sum current transformer	4-pin modular connector
- voltage output	Ø 0,16" (4 mm) socket (front panel)
Weight	1.5 lb (680 g)

Measuring Characteristics
Channels	8
Measuring range	1 mA - 12 A 50-60 Hz
Resolution	-I < 1 A, 1mA -I > 1 A , 10 mA
Accuracy with
- VMI-xx	+5% (closed core) + 1-2 dgt
- VMIK-xx	+10% (split-core) + 1-2 dgt
- Window type transformers	+20% (split-core) + 1-2 dgt, repeatability +2%
Setup
- alarm range	5 mA – 10 A
- alarm delay	up to 95 s
- hysteresis	0-90% alarm level
AC-output
- correspondence	1mVAC=1mAAC
- linear measuring range	1mA-2.5 A, accuracy with VMI transformers (closed core) +5% VMIK transformers(split-core) +10%

Alarm Relay
relay connection	two potential free, change-over contactors
Imax	max 5 A
Vmax	250 V AC
Vmax	24 V DC

DIMENSIONS