Quick measurement

 


      Without shutting down drains
 


      Portable clamps
 


      Immune to interference
 


      Detection of all types of short circuits
 


      High accuracy independent of network capacity
 


      Short-circuit detection between batteries and drains of two sections

 

Challenges in DC networks

DC networks are one of the most responsible systems in electric power plants. Their failure-free operation determines the correct work of control, regulation, measurement and protection systems for power and technological processes

These networks are often very extensive, their length reaches even up to 100 km. They are therefore highly exposed to the adverse effects of external factors affecting the deterioration of insulation. The most frequent causes causing weakening of the network insulation, and consequently the occurrence of short circuits, include

  • dirt or moisture,
  • mechanical damage,
  • ageing,
  • negligence during installation works and periodical inspections and tests.

Short circuits in direct current networks cause failure or incorrect operation of APiA systems and control and protection systems. They are a threat to human health and life.

Continuous control of insulation resistance, as well as precise localisation and quick removal of short-circuits in these networks is a particularly important issue. In traditional practice, the "voltmeter method" or measuring relays are used to check the insulation state. Localisation of short-circuits is carried out by switching off successive parts of the network, and in extreme cases by intentional short-circuiting of the opposite pole of the network. Due to the interference introduced in the DC network, these methods are cumbersome and often impossible to apply during the operation of the equipment. They do not ensure quick and effective elimination of short circuits, nor do they enable preventive actions.

System description

The DCtest2 microprocessor-based network monitoring system is designed for insulated networks from 24 to 220V. Correct operation (accurate measurement of insulation resistance, precise location of earth faults) of the system in conditions of large disturbances occurring in DC networks is possible thanks to the use of modern systems of compensation and filtration of measurement signals. The system controls (measures) the insulation resistance of the network and measured outlets against the ground and other galvanically earthed circuits (e.g. 230/400V AC).

The system is applicable to any DC network regardless of its configuration. The measurement results are available on the LCD display of the central unit. They can also be transmitted to a supervisory supervisory and control system.

System construction:

The system consists of the following components:

  • central unit (symbol DC2-jc);
  • 9 mm (DC2-I9), 13 mm (DC2-I13) and 43 mm (DC2-I43) diameter stationary measuring transformers;
  • concentrators (symbol: DC2-k) to which stationary measuring transformers are connected (max 8 transformers to one concentrator);
  • a portable locator (symbol: DC2-p.)

Below the idea of system operation is presented:  

The main elements of the system are placed in the central unit. The central unit is preferably installed on the switchgear facade or in the control room. Measuring transformers and concentrators should be built in the DC switchgear. Elements of the measuring system are connected with the central unit via communication link RS485.

Central unit DC2-jc

The central unit is the basic element of the system and is equipped with:

  • a system for calculating the insulation resistance of the entire network;
  • two measuring elements R<t that control the value of the network resistance;
  • equipped with additional delay members;
  • the internal signaling system;
  • External signaling system;
  • The system for visualization of the measurement results with the LCD display;
  • Communication system with concentrators;
  • communication system with other central units

DC2-k concentrator

Current signals measured by measuring transformers are introduced to the concentrator, where the value of the earth fault current is calculated. The ground fault current and the resistance of the individual outlets can be read off on the display.

DC2-I9, DC2-I13, DC2-I43 stationary measuring transformers

Earth leakage currents of individual outlets are measured by measuring transformers installed in the measured outlets. The number of measuring transformers in the system depends on operation needs, i.e. how many outlets have to be metered. Up to 100 transformers (optionally up to 200 transformers) can be connected to one central unit.

DC2-p portable locator

The portable locator is a supplement to the stationary system of locating short-circuits and is used to measure insulation in places where stationary measuring transformers are not installed and to precisely locate a short-circuit point. It is equipped with current clamps, with which both conductors (positive and negative) should be covered during the measurement. The locator indicates the value of the earth fault current. The operator, by measuring successively the currents of individual points of the circuit, locates the point of deteriorated insulation resistance.

DCtest2 basic features

  • detects all types of short circuits: metallic, through a relay coil, two simultaneous short circuits, short to earth, short circuits to other galvanically earthed networks e.g. 400/230V
  • internal resistance of impulse generator (20kOhm) does not cause activation of auxiliary relays;
  • the pulse generator frequency is selected depending on the DC network capacitance;
  • measurement of insulation resistance of the whole DC network and individual outlets is carried out simultaneously;
  • delay of signalling activation by several dozen seconds in order to verify the measurement results;
  • large, easy to read display, on which the value of insulation resistance of the whole network and the values of resistance of the measured outlets are given
  • verbal description of the outlets being measured;
  • two independent adjustable signaling degrees of lowering of insulation resistance;
  • signaling of system equipment damage: sensor damage, concentrator damage;
  • communication with control and supervision system by protocols: Modbus RTU, Modbus TCP, IEC 103

Benefits resulting from the use of DCtest2

  • ensures quick location of an earthed drain;
  • enables preventive actions;
  • eliminates risk to human health and life;
  • prevents dangerous and costly outages of technological equipment;
  • protects the network against insulation degradation


The system is used in power plants, CHP plants, industrial plants and distribution substations of the National Power System