Earthing / Grounding Issues - PowerPoint PPT Presentation

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Earthing / Grounding Issues

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  1. Earthing / Grounding Issues Reasons for Earthing and Bonding • Detect fault current and fast removal of power source at fault • Prevent potential differences which may cause electrocution or sparks • Minimise the effect of lightning strikes • Prevent build-up of ESD • Minimise the effect of electrical interferences • Meet Explosion-Proof apparatus safety requirements Reference: MTL website

  2. Earthing / Grounding Issues Ground / earth resistance and resistivity should be measured when: • Installing new ground systems and electrical equipment • Periodically testing of ground and lightning protection rods • Prior to design of ground protection systems

  3. Earth Testing Methods • Fall of Potential – 3 and 4 Pole Testing • Resistivity • Selective Testing • Stakeless Testing

  4. Earth Testing Methods (1) Fall of Potential – Three and Four Pole Testing

  5. Earth Testing Methods (1) Fall of Potential – Three and Four Pole Testing

  6. Earth Testing Methods (1) Fall of Potential – Creating the ‘S’ Curve • The positioning of temporary electrode for the test is a critical issue • The distance between electrodes is dependant on the ‘pool of potential’ of the earth system under test • Distances of temporary electrode should be varied to plot values as an ‘S’ curve

  7. Earth Testing Methods (2) Resistivity Measurement From the indicated resistance value RE, the soil resistivity calculates according to the equation : E = 2 p . a . R E E ...... mean value of soil resistivity (W.m) RE ...... measured resistance (W) a ...... probe distance (m)

  8. Principle: Wenner – Method Measurement of specific earth resistance  The measuring method according to Wenner determines the soil resistivity down to a depth of approx. the distance "a" between two earth spikes. By increasing "a", deeper layers can be measured and checked for homogeneity. By changing "a" several times, a profile can be measured from which a suitable earth electrode can be determined. According to the depth to be measured, "a" is selected between 2 m and 30 m. This procedure results in curves:

  9. Earth Testing Methods (2) Resistivity Measurement Curve 1:As E decreases only deeper down, a deep earth electrode is advisable Curve 2:As E decreases only down to point A, an increase in the depth deeper than A does not improve the values. Curve 3:With increasing depth E is not decreasing: a strip conductor electrode is advisable.

  10. Earth Testing Methods (3) Selective Measurement Method

  11. Earth Testing Methods (3) Selective Measurement Method

  12. Measured voltage Im Measured current IM Auxiliary earth electrode Probe Earth Testing Methods (3) Principle: Selective earth measurements Advantage: Distinct earth resistances within meshed ground systems can be measured without disconnection. Only clamp current Im is used for calculation of RE. Important: The minimum clamp current is 0.5mA – if not, an error message is displayed. R Display = R E3 !!

  13. Earth Testing Methods (3) Selective Measurement Method on High Tension Towers

  14. Earth Testing Methods (3) Measurements on high tension towers • Applicable for nearly all metal constructions! • Example: Tower with four stands. • Important: Do not move the current injection point (E) during test! • All stands are tested in sequence with the split core transformer. split core transformer ring earth electrode

  15. Earth Testing Methods (3)

  16. Earth Testing Methods (4) Application: Function RE selective SATURN GEO X, SATURN GEO plus Only the current from the current clamp is used for calculation of RE. The precise value of RE is on display! Connection to equi- potential bus bar Equi Potential bus bar sum Earth electrode Auxiliary earth - (H) Probe - (S) Water pipe RE (injection of test current) (voltage reference) R E Water pipe I I = I + I E Water pipe sum E E Water pipe RDisplay= U / IE = RE

  17. Earth Testing Methods (4) Stakeless Measurement Method

  18. Earth Testing Methods (4) Stakeless Measurement Method

  19. Earth Testing Methods (4) Stakeless Measurement Method

  20. Earth Testing Methods (4) Stakeless earth loop measurements I I Current amplifier Voltage source U Rn Rx Rn= m earth resistances in parallel Assume that there are Rn resistances in parallel (e.g. in meshed ground systems, telecom, electric power distribution systems) earth connections are inter-connected. Thus Rn<<Rx is valid. Rn is negligible and the measuring loop resistance is mainly Rx. In this case the value on display of the ground loop tester is exactly Rx.

  21. For all applications with at least two earth electrodes...e.g. high tension towers, meshed grounding systems, telecom-cables ...... Erder Earth Testing Methods (4) Principle: Stakeless earth measurements • Simply put both clamps around conductor, cable, pipe etc. • Clamps with a large variety of openings are available. Adapter – for GEO X only black red Earth electrode > 10cm

  22. Earth Testing Methods (4) Example: Stakeless earth measurement