GB/T 18216.8-2015Electrical safety in low voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. -- Equipment for testing, measuring or monitoring of protective measures -- Part 8: Insulation monitoring devices for IT systems (English PDF)

3.1 External DC voltage

A DC voltage (generated by a DC component) between an AC conductor and ground in an AC system.

3.2 Insulation resistance

The ground resistance of the monitored system, including the ground resistance of all connected equipment.

3.3 Specified response value

The insulation resistance value is fixed or adjustable on the insulation monitoring device, and it is monitored whether the insulation resistance drops below this limit.

3.4 Response value

Under specified conditions, the insulation resistance value of the insulation monitoring device responds.

3.5 Relative uncertainty

The response value is subtracted from the specified response value and then divided by the specified response value and multiplied by 100%, which is expressed as a percentage.

3.6 System leakage capacitance

The maximum allowable value of the total capacity of the monitored system to ground (including all electrical equipment connected to the system), below this value The device can work as specified.

3.7 Rated contact voltage

Rated voltage at which the relay contacts open and close under specified conditions.

3.8 Response time

The time required for the insulation monitoring device to respond under the conditions specified in 6.1.2.

3.9 Measuring voltage

The voltage appearing on the measurement terminal during measurement.

Note: Supplementary explanation to the definition given in IEC 61557-1, the measured voltage (Um) is the terminal of the monitored system and the protective conductor terminal without fault and no current The voltage that appears between.

3.10 Measuring current

The maximum current that can flow between the system and ground is limited by the internal resistance Ri of the measuring voltage source of the insulation monitoring device.

Note: The measured current is called injection current in IEC 60364-7-710.

3.11 Internal impedance

The total impedance of the insulation monitoring device measured at the nominal frequency (connected) between the terminal of the monitored system and the ground terminal.

3.12 DC internal resistance

Resistance (connection) between the terminal of the monitored system and the ground terminal on the insulation monitoring device.

3.13 Functional grounding; FE

The grounding of one or more points in the system, device or equipment is for the functional needs of the device in addition to electrical safety.

Note: For insulation monitoring devices, functional grounding is the measurement connection to ground.

5.1 Logo

In addition to the signs specified in IEC 61557-1 on the insulation monitoring equipment, the following signs shall be provided.

5.1.1 The type of device and the mark of origin or the name of the manufacturer.

5.1.2 The IT system being monitored (if the insulation monitoring device is used for a specific type of IT system).

5.1.3 Wiring diagram, or the number of the wiring diagram, or the number of the operation guide.

5.1.4 Nominal system voltage Un or range of nominal voltage.

5.1.5 Nominal value of rated power supply voltage Us, or working range of rated power supply voltage.

5.1.6 Nominal frequency of rated power supply voltage Us, or working range of rated power supply voltage frequency.

5.1.7 Specify the response value Ran, or the minimum and maximum response values Ran; if applicable, specify the range of response values, within this range, relative (percent The ratio) uncertainty is higher than the values listed in Table 1.

5.1.8 Mandatory external signs, if necessary, can be listed inside the device. serial number, year of manufacture or model identification.

The data given in 5.1.1 must be permanently marked on the insulation monitoring device, and the method of marking shall ensure that These signs are still clearly visible after installation.

5.2 Instructions for use

In addition to the instructions given in IEC 61557-1, the instructions should also provide the following.

5.2.1 The internal impedance Zi of the measuring line as a function of the nominal frequency.

5.2.2 When the rated supply voltage is the nominal value Us, the peak value Um of the measured voltage shall meet the requirements of Table 1.

5.2.3 When the measuring terminal is short-circuited, the maximum value Im of the measured current shall meet the requirements of Table 1.

5.2.4 Technical data for connecting the external alarm device interface, including the description of rated voltage and current, rated insulation voltage and interface functions.

For contact circuits, the data should refer to the standards IEC 61810-2 or IEC 60947-5-1 and IEC 60947-5-4.

5.2.5 Note that insulation monitoring devices should not be connected in parallel (eg when multiple systems are connected together).

5.2.6 When the wiring diagram is not marked on the device in accordance with the requirements of 5.1.3, the wiring diagram shall be provided.

5.2.7 Information on the effect of the system leakage capacitance Ce and its allowable maximum.

5.2.8 Externally added DC voltage (Ufg) of any polarity that can continuously act on the insulation monitoring device without causing damage.

5.2.9 The test voltage required by 4.9 and meet the relevant EMC standards.

5.2.10 According to the requirements of 5.2.4, the electrical data of the contact circuit.

5.2.11 Measure the internal resistance Ri of the line.

6.1 Type test

The type test shall be carried out in accordance with the requirements of 6.1.1 to 6.1.7.

6.1.1 Response value

The response value test shall be performed on the specified nominal voltage Un and the rated power supply voltage Us minimum and maximum. When testing, the insulation resistance shall be simulated as follows.

--- Unipolar (from a certain phase of Un);

--- Symmetric (all phases with the same resistance from Un).

The test measuring device should be able to adjust slowly, continuously or in small steps when simulating the insulation resistance, and add a parallel leakage Leakage capacitance. When simulating the leakage capacitance of the system, the insulation resistance of the capacitor used should have at least 100 times the specified response value and its maximum The maximum allowable deviation limit is 10%. During the test, the test resistance should start from a high value and slowly decrease.At the same time, observe the operation of the insulation monitoring device.

Line situation. When determining the response value, the insulation resistance presented by the test circuit and its inherent leakage capacitance should be taken into account.

When the specified response value of the insulation monitoring device is continuously adjustable, or with a digital setting without a mechanical switch, it should be at least within the setting range Check the compliance with the conditions listed in Table 1 at 5 points within the range. This check should be roughly averaged at each end point and within a set range At various points of the distribution. This method is also applicable to a setting device without a switch.

If the specified response value is set by a mechanical switch method, each stage should be tested. The initial test should be performed at The line does not contain any system leakage capacitance, and the test resistance should be slowly reduced in order to find the steady-state response value.

The manufacturer should provide detailed instructions.If the measurement method is affected by the leakage capacity Ce of the system, the electricity should be inserted in steps The method of the container is checked to determine whether the limits shown in Table 1 are met within the range of capacitance indicated by the manufacturer. Should be determined To uncertainty.

6.1.2 Response time

Under the condition of 1µF leakage capacitance Ce and nominal system voltage, the insulation resistance value suddenly decreases from near infinity to the minimum When the value is 50% of Ran, test the operation delay time of the output circuit.

6.1.3 Measuring the peak value of the voltage Um

The peak voltage test shall be used to check whether the requirements given in Table 1 are met, and whether the instructions in 5.2.2 are applicable. Voltage measuring instrument The internal resistance should be at least 20 times the DC internal resistance Ri of the measurement circuit.

6.1.4 Internal resistance and impedance

The following tests shall be used to check compliance with the requirements specified in Table 1. These tests can be performed with or without rated power Under the source voltage Us, an appropriate measurement voltage is applied between the interconnected system terminals and the ground terminal. Uncertainty of the measuring device Degree limit value should not exceed 5% under reference conditions.

6.1.4.1 Internal impedance Zi

To confirm that the internal impedance Zi meets the requirements of Table 1, its voltage source should be consistent with the nominal system voltage Un, and its frequency should be equal to the nominal System frequency, its harmonic coefficient should be lower than 5%, and internal resistance should be lower than 10 ohm.

From the resulting peak-to-peak current Ipp, the following formula is used to calculate the internal impedance.

6.1.4.2 DC internal resistance Ri

To confirm that the DC internal resistance meets the requirements of Table 1, the DC voltage should have the same order of magnitude as the nominal system voltage Un, but must not exceed Allowable maximum external DC voltage Ufg. The following formula should be used to calculate the DC internal resistance Ri from the generated current I.

6.1.5 Equipment indicating insulation resistance

When the insulation monitoring device is provided with equipment indicating the insulation resistance, a test shall be carried out in accordance with the requirements of 4.7 to check the manufacturer's requirements. Whether the uncertainty limit is met.

6.1.6 Dielectric strength test

The insulation monitoring device shall be tested in accordance with the requirements of IEC 61010-1.

6.1.7 Electromagnetic compatibility (EMC)

The electromagnetic compatibility test shall be performed in accordance with the requirements of 4.11.

6.2 Routine tests

Routine tests shall be performed on each insulation monitoring device.

Note: If the method of technical failure analysis and/or statistical analysis can be used to prove that the failure rate is low in serial production, the routine test can be limited.

System is to simplify the sampling test. All routine tests should be performed during manufacturing or at the end.

6.2.1 Response value

The relative uncertainty of the response value shall be routinely tested in accordance with the requirements of 6.1.1. In this test, the following conditions shall apply.

--- room temperature (23 °C ± 3 °C);

--- 1.0 times Un and 1.0 times Us, or for devices with several rated voltages, according to the highest rated voltage Un or Us;

--- Ce = 1µF.

In this test, the limit value should be reduced as far as possible until the conditions in Table 1 can be met. When the insulation monitoring device has a continuously adjustable specified response If the value is correct, the operation should be checked at least three points within the setting range. When checking, set the start and end points of the range As well as the intermediate points. When the specified response value is selected by means of mechanical switches, each stage should be an examination.

6.2.2 Performance of the test device

The internal test button and external test button (if equipped) should be checked to see if they are operating normally and in accordance with Claim. […]

6.2.3 Equipment indicating insulation resistance

In accordance with the requirements of 4.7, when the insulation monitoring device contains equipment indicating insulation resistance, it... […]