Page 58
.), the possibility switching off the power supply, the area available for setting stakes, etc., stipulate the general installation conditions applied order guarantee the safety people, pets, farm animals and property protecting them against the hazards and damage which may result from use the electrical installations. and are known values, the loop resistance can deduced from them.theorY applications
Technical overview
EARTH MEASUREMENT
For residential industrial installations, the presence earth connection one the basic rules ensure that the electrical installation safe.
100 0
Earth electrode tested
R1
R2
Rn-1
Rn
Schematic diagram: earth clamp
H ES
2) Line-PE loop measurement (only system) urban environments, often proves difficult measure earth resistances using auxiliary stakes because Fuses RCD not possible set the stakes for reasons space, concreting, etc.
List the different earth measurement methods
Single earth connection 3-pole method alias method Triangle method stakes) 4-pole method Variant method stake) Line-PE loop measurement Network multiple parallel earths Selective 4-pole method Earth clamp Earth loop measurement with clamps Rural building with possibility setting stakes Urban building with possibility setting stakes
3) Selective earth measurements For interconnected earths, selective earth measurement can used for quick, safe testing. Note: (impedant) systems, the loop impedance measurement can used calculate the short-circuit current and thus size the protective devices correctly. Rtransfo Rearth Statistics from the field have shown that the ideal method for guaranteeing the highest possible measurement accuracy involves placing the stake point the distance from the line EH. For correct measurement, the stake should least metres away from the earth tested. For the earth clamp and for the 2-clamp method, all you have find out the earth value and the value the currents flowing clamp the cable connected the earth. addition the earth measured, the loop resistance measured this way includes the earth and internal resistance the transformer and the resistance the cables. When there large enough area available set stakes, earth measurement should carried out with the traditional 3-pole method, also known the method.
n (only with system) n
Here overview the most frequently-used measurement methods: The 62 % in-line measurement method (two stakes) This method requires the use two auxiliary electrodes Fuses RCD (or "stakes") allow current injection and provide the 0 V reference potential. However, the presence earth connection does not guarantee safety and, even the earth correctly sized, only regular testing can ensure that functions correctly. This case involves network parallel earths. You must then make sure that the measurement does not vary significantly when moving the stake ± 10 (S’ and S”) either side its initial position, while remaining the line EH. The standards concerning electrical installations consider that the loop resistance (overall earth resistance) may taken into account instead the earth resistance comply with the rules protection against the risk indirect contacts. For more accurate measurement, possible use 4-pole measurement method (adding connection between the earth tested and the terminal the measurement instruments) minimize the resistance the measurement leads, thus improving accuracy. This method strongly recommended for low resistance values the influence measurement-lead resistance will then considerable. The actual earth resistance therefore lower: Rmeasured Rearth. The positioning the two auxiliary electrodes relation the earth connection tested DDR E(X), crucial. There are large number different methods for earth measurements, however, and the right choice depends the type neutral system, the type installation (residential, industrial, urban, rural, etc.A 6472
Schematic diagram: 2-clamp method also possible use the 4-pole clamp method, which requires auxiliary stakes but allows precise measurement the earth resistance. earth clamp comprises two windings: generator winding and receiver winding: The clamp's "generator" winding develops voltage the constant level around the clamped conductor; current Rloop then flows through the resistive loop. this case, not necessary isolate the installation (no need open the earth bar) and, for loop measurements with clamps with earth clamp, not necessary set stakes. For correct measurements, the "auxiliary connection" providing the reference potential (S) must not positioned the areas influenced earths due the flow the current (i). the measurement varies, means that (S) influence area, the procedure should repeated after increasing the distances.
RE
E
C. This method may more practical places where access difficult when larger clamping diameter required. Loop measurement can then used test earths urban environments without using stakes simply hooking the mains power supply (mains DDR socket). The standards for electrical installations, such IEC 60364, 15-100, etc. One clamp acts the generator, while the second acts the receiver. all these resistances are very low, the value Rtransfo Rearth measured overall earth resistance value. The (overall) measurement error introduced this method actually contributes greater safety. Knowing that "n" resistances parallel are equivalent resistance Raux with negligible value, can measure the local earth value Rx: Rloop Raux (where Raux resistance equivalent R1…Rn parallel) Raux’, obtain the result Rloop The 2-clamp method equivalent method. The absence earth connection may endanger people's lives and damage electrical installations and property. The "receiver" winding measures this current
