Definition: An instrument used to measure ground resistance is called a ground resistance tester. All equipment in the power system is grounded by grounding electrodes. Grounding protects equipment and personnel from fault currents. The earth's resistance is very low. The fault current flowing through the grounding electrode flows to the earth. Therefore, protect the system from damage.

The ground electrode controls the device's high potential, which is caused by high lightning surges and voltage spikes. The neutral point of the three-phase circuit is also connected to the ground electrode for protection.

Before grounding equipment is provided, it is necessary to determine the resistance in the specific area from which the grounding pits can be dug. The ground should have low resistance so that the fault current flows easily to the ground. The ground resistance is determined by the ground tester.

Structure of grounding resistance tester

The ground resistance tester USES a manual generator. The rotating current reverser and rectifier are two main parts of a globe. The current reverser and rectifier are mounted on the shaft of the DC generator. Due to the use of rectifier, the grounding resistance tester can only work on the DC.

The tester has two commutators, current reverser and rectifier. Each commutator consists of four fixed brushes. A commutator is a device for changing the direction of current. It is connected in series with the armature of the generator. And the brush is used to transfer power from the fixed part of the device to the moving part.

The brushes are arranged in such a way that they are alternately connected to one of the sections even after the commutator has rotated. The brush and commutator are always connected to each other.

The globe consists of two pressure and current coils. Each coil has two terminals. A pair of pressure coils and current coils are placed across the permanent magnet. A pair of current and pressure coils are short-circuited and connected to the auxiliary electrode.

One end of the pressure coil is connected to the rectifier and the other end to the ground electrode. Similarly, the current coil is connected to the rectifier and the ground electrode.

The ground resistance tester consists of a potential coil connected directly to a dc generator. The potential coil is placed between the permanent magnets. The coil is connected to the pointer, which is fixed on the calibration scale. A pointer indicates the size of the ground resistance. The deflection of the pointer depends on the ratio of the voltage of the pressure coil to the current coil.