Skip to main content

Explain Insulation Resistance : How Insulation resistance is measured

Insulation resistance (IR) of an electrical equipment refers to the resistance between conducting part and earth.
It is expressed in MW
It can also be measured between two circuits separated by insulation
It is measured by Insulation measurement kit(Megger). (500/1000/2500/5000V)
IR reveals quality of insulation of the equipment and the degree of dryness/ moisture.
The subsequent high voltage test can be avoided if IR is low.

How to measure Insulation resistance  

Megger consists of a built in mega ohm meter and a D.C. generator.
The generator is driven by hand or by a motor.
One terminal of megger is connected to conducting part and the other terminal is connected to earth frame.
The rotor of the generator is driven by hand or motor.
The reading  ( Vdc/ Idc)  read by the megger  gives IR value in MW.
The scale of megger is graduated from 0 to ยต in MW.
When D.C. voltage is applied to the insulation, initially the insulation draws capacitive charging current (Ic) in addition to leakage current( IL)
Initial megger reading  Ro = Vdc / Idc = Vdc / ( Ic + IL)
After continuous application of D.C. voltage, the capacitive current reduces and only leakage current continue.
Megger  reading after 60 seconds will be  R60= Vdc/Idc
Since IL< Ic + IL,   R60 > Ro
 
Labels:

Popular posts from this blog

Right Of Way / Way Leave Clearance for various Electrical Power Transmission Line

Width of maximum right of way permitted as per forest conservation act ‘1980 and its subsequent amendment dated 25 th October, 1992, are as per Table 1.  Researches are being carried out for further optimizing the Right of Way. Guidelines of forest environmental rules shall be followed to avoid excessive tree cutting i.e. all the trees should be cut from root level in the 3 m corridor below each line conductor / earth wires.  In the balance corridor, trees branches are only to be lopped to attain the specified clearance as per Table 1. Table 1  – Guidelines for Right of Way as per forest conservations act 1980 and subsequent amendment dated 25 th October, 1992 Line voltage (kV) 66 110 132 220 400 500 HVDC 765 Row width (Meter) 18 22 27 35 52 52 85 Electrical clearance:   Electrical clearance while power lines crossing each other. In case of power line crossings, minimum clearance between lowest conductor of line and ground wire / top conductor of ...
Read more

What is CSD (Controlled Switching Device) in Electrical System

Definitions CSD (Controlled Switching Device): A device that is installed at the relay and control panel to overcome the transient behaviour of voltage and current during switching. This device synchronizes the switching of each pole of the circuit breaker according to the zero crossing of the corresponding phase. This device is also known as a phase synchronizing device, or PSD for short. Requirement When we switch off an online circuit breaker to disconnect an inductive load, we ideally want to interrupt the current of the system at the zero crossing of the current waveform. However, this is practically impossible to achieve. In a normal circuit breaker, the current interruption may occur near the zero crossing point, but not exactly at it. Since the load is inductive, this sudden interruption of current causes a high rate of change of current (di/dt), which results in a high transient voltage in the system. In low or medium voltage power systems, this transient voltage during circui...
Read more

Roles and Responsibilities of SLDC- State Load Dispatch Center in India

As per section 33 of Electricity Act – 2003 (Central Act 36 of 2003), SLDC-State Load Dispatch centers performs:- SLDC- State Load Dispatch Center suppose to carry out following functions or Roles and Responsibilities of State Load Dispatch Center. Scheduling: All Open Access users (excluding wind and mini hydel and generating stations having total capacity not less than 5 MW and up to 15 MW opting for injection under UI) that are connected to the Grid shall schedule and dispatch according to instructions given by SLDC. The methodology of scheduling shall be according to provisions of Gujarat State Grid Code and Clauses 26 and 44 of GERC Tariff Regulations. Gaming: SLDC should see that no gaming is done while declaring capacity by generators. Energy Accounting: A State Energy Account, for the billing and settlement of ‘Capacity Charge’, ‘Energy Charge’, ‘UI Charge’ and ‘Reactive Charge’ shall be prepared by the SLDC. The SLDC...
Read more