Free Expert Guides on Power Systems, Circuit Design & Electrical Troubleshooting

What are Electrostatic Type Instruments?Electrostatic Instrument DefinitionAn electrostatic instrument is defined as a device that uses static electrical fields to measure voltage, usually high voltages.Working PrincipleAs the name suggests, electrostatic instruments use static electrical field to produce deflecting torque. They are typically used to measure high voltages but can also measure lower voltages and power in some cases. There are two ways the electrostatic force can act.Construction

PMMC Meter DefinitionA PMMC meter (also known as a D’Arsonval meter or galvanometer) is defined as a device that measures the current through a coil by observing the coil’s angular deflection in a uniform magnetic field.PMMC ConstructionA PMMC meter (or D’Arsonval meters) is constructed of 5 main components: Stationary Part or Magnet System Moving Coil Control System Damping System MeterWorking PrincipleA PMMC meter uses Faraday’s Laws of electromagnetic induction, where a current-carrying condu

Errors in Measurement DefinitionErrors in measurement are defined as the differences between measured values and true values.Static Error FormulaStatic error is calculated using the formula dA = Am – At, where dA is the error, Am is the measured value, and At is the true value.Limiting ErrorsThe concept of guarantee errors can be cleared if we study this kind of error by considering one example. Suppose there is a manufacturer who manufactures an ammeter, now he should promise or declare that th

What are Electrical Measuring Instruments?Electrical Measuring Instruments DefinitionAn electrical measuring instrument is a tool used to measure electrical parameters.Absolute Measuring InstrumentsAbsolute measuring instruments provide output based on the physical constants of the instruments. Examples include Rayleigh’s current balance and the Tangent galvanometer.Secondary Measuring InstrumentsSecondary measuring instruments are made using absolute instruments and are calibrated by comparing

What is the Measurement of Resistance?Resistance DefinitionResistance is the opposition to electric current flow, a fundamental concept in electrical engineering.Measurement of Low Resistance (<1Ω)Kelvin’s Double BridgeKelvin’s double bridge is a modification of simple Wheatstone bridge. Figure below shows the circuit diagram of Kelvin’s double bridge.As we can see in the above figure there are two sets of arms, one with resistances P and Q and other with resistances p and q. R is the unknown

Induction Type Meters DefinitionInduction type meters are devices used to measure electrical energy in homes and industries by using the interaction of fluxes and alternating currents.Working PrincipleThe working principle andconstruction of an induction type meter are simple and easy to understand, making them popular for measuring energy in homes and industries. In all induction meters, two fluxes are produced by different alternating currents on a metallic disc. These alternating fluxes creat

What is a Motor Protection Relay?Motor Protection Relay DefinitionA motor protection relay is a device used to detect faults and protect high voltage induction motors by isolating faulty parts.Common FailuresMotors can fail due to thermal stress, single phasing, earth faults, short circuits, locked rotors, and bearing issues.HT Motor ProtectionMotor protection relays for high voltage motors provide protections like thermal overload, short circuit, single phasing, and earth fault protections. Mot

What is Inverse Time Relay?Inverse Time Relay DefinitionAn inverse time relay is defined as a relay where the operation time decreases as the actuating quantity increases.Operating Time RelationshipThe relay’s operating time is inversely proportional to the magnitude of the actuating quantity, meaning higher quantities result in faster relay operation.Mechanical AccessoriesInverse time relays use mechanical accessories, such as a permanent magnet in an induction disc relay or an oil dash-pot in

What is Distance Protection Relay?Impedance Relay DefinitionAn impedance relay, also known as a distance relay, is defined as a device that triggers based on the electrical impedance measured from a fault’s location to the relay.Working Principle of Distance or Impedance RelayImpedance RelayWorking Principle : The operation of an impedance relay is straightforward. It uses a voltage element from a potential transformer and a current element from a current transformer. The relay’s action depends

What is an Over Current Relay?Overcurrent Relay DefinitionAn overcurrent relay is a protective device that operates solely based on current without the need for a voltage coil.Working Principle of Over Current RelayThe core component of an overcurrent relay is a current coil. Under normal conditions, the coil’s magnetic effect is too weak to overcome the restraining force and move the relay’s element. However, if the current increases sufficiently, its magnetic effect intensifies, surpassing the