Residual current electrical fire monitoring system principle and installation precautions

Tag: Security detector Alarm Controller for current transformer

1 Prevention of electrical fire

In order to prevent and reduce electric fire, the insulation status of 220/380 V power supply line should be monitored online, and the electric fire monitoring system can be used for leakage detection and alarm. Electrical circuit or electrical equipment once the leakage and exceed the rated value, the alarm immediately issued a sound and light alarm signal and display leakage current size. From the occurrence of grounding arc to the cause of fire and the spread of fires, it will take some time, this time to check and eliminate the failure forecast, can effectively avoid the occurrence of electrical fire. Alarm but do not cut off the power supply, you can avoid the power switch tripping caused the entire building blackout, both to ensure the safety of electricity and ensure the uninterrupted power supply.

In order to ensure the safety of people's lives and property, strict implementation of the GB 13955-2005 "residual current action protection device installation and operation" Provisions of the precautionary measures, in the building of the power supply line and the trunk of the installation of electrical fire Monitoring system is very necessary.

2 electrical Fire Monitoring System principle

2.1 Principle Block Diagram

Monitoring system is a current transformer, monitoring detector, alarm or controller of electrical fire real-time monitoring and implementation of alarm or cut off the power supply device, the system is composed of block diagram 1 shown.

3 Installation method of electrical fire monitoring system

3.1 Total residual current detection in low voltage distribution system

If you want to monitor the overall insulation state of the system, the total residual current of the system can be detected, provided that the unit needs to have an independent power-changing system. The current transformer is installed in the transformer grounding line to provide residual current, detectors, alarms can be selected split or integrated structure, 6.

This kind of residual current detection requires the grounding form of the power supply system to be tn-s.

3.2 Trunk Residual current detection

Trunk refers to the main branch of low-voltage distribution lines, this kind of installation is relatively simple, the current transformer is installed in the trunk line, the detection signal is the transformer after the line and the residual current generated by the load, 7 shown.

3.3 Multi-route residual current detection

Take the 8-way test as an example: 8 current transformers are installed on each of the output lines of the switchboard as shown in 8 (a) and (b).

6 Precautions for installation of electrical fire Monitoring system

6.1 Grading Protection

In order to reduce the scope of the power outage caused by personal electric shock and grounding fault, it is usually necessary to install a three-stage (or two) residual current protection device at different locations of the power supply line to form a graded protection. According to the power load and circuit conditions, generally sub-level two or three protection. Applicable to urban and rural first and second level protection, the specific installation drawings in GB 13955-2005 has been clearly defined.

6.2 Installation Precautions

6.2.1 System Residual current detection

In the system grounding type for the tn-c-s system, the transformer low-voltage side outlet is a pen wire to the ground is insulated.

When the pen is divided into N-line and PE line via terminal block, the N line is no longer grounded. At this time, the current transformer must be installed in the pen line into the PE line, the N-line of the PE line on the middle segment, 6.

Residual current detection of 6.2.2 trunk line

For the power supply system, the current transformer as long as the two cable to cover, requires that the N line is not repeated grounding.

For 380 v distribution system, the current transformer must be at the same time to cover the L1, L2, L3, n lines, PE wire must not pass through the transformer, and the n line thereafter shall not be grounded.

In the grounding type of tn-c system, it must be converted to Tn-c-s, tn-s or local TT system, before the use of alarm-type residual current protection device can be installed.

Installation of 6.2.3 Transformer

The current transformer should be installed easy to access the place, the installation of the transformer has no direction problem. Plug-in transformer installation without disconnection, power, transformer can be directly hung on-line, can also be fixed on the switchboard, but installation should pay attention to safety.

6.2.4 setting of alarm value

Residual current alarm Set value must be greater than the leakage current value of the circuit under test, can use the pre-check function of the device to detect the actual leakage current value of the measured circuit, usually alarm setpoint value is not less than twice times the leakage current value.

Residual current electrical fire monitoring system principle and installation precautions