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

In practical work, insulation resistance of distribution transformers is generally measured twice: the insulation resistance between thehigh-voltage (HV) windingand thelow-voltage (LV) winding plus the transformer tank, and the insulation resistance between theLV windingand theHV winding plus the transformer tank.If both measurements yield acceptable values, it indicates that the insulation among the HV winding, LV winding, and transformer tank is qualified. If either measurement fails, pairwise

1 IntroductionPower transformers are among the most critical equipment in power systems, and it is essential to maximize prevention and minimize the occurrence of transformer failures and accidents. Insulation failures of various types account for more than 85% of all transformer accidents. Therefore, to ensure safe transformer operation, regular insulation testing of transformers is necessary to detect insulation defects in advance and promptly address potential accident hazards. Throughout my

Standard for Loop Resistance of Vacuum Circuit BreakersThe standard for loop resistance of vacuum circuit breakers specifies the required limits for the resistance value in the main current path. During operation, the magnitude of loop resistance directly affects the safety, reliability, and thermal performance of the equipment, making this standard critically important.Below is a detailed overview of the loop resistance standard for vacuum circuit breakers.1. Significance of Loop ResistanceLoop

Diode Resistance Resistance opposes the flow of current through a device. Diode resistance is the effective opposition a diode offers to current flow. Ideally, a diode offers zero resistance when forward biased and infinite resistance when reverse biased. However, no device is perfect. Practically, every diode has small resistance when forward biased and significant resistance when reverse biased. We can characterize a diode by its forward and reverse resistances.Forward ResistanceEven with forw

What is Rotor Resistance Control of Induction Motor?Rotor resistance control definitionRotor resistance control is defined as a way to manage the speed of an induction motor by adjusting the resistance in its rotor circuit.Induction motor basicsThe working principle of the universal induction motor is that the motor speed can be adjusted by changing the resistance of the rotor.Speed control of induction motorSpeed control is essential for applications that require variable motor speeds and can b

Winding Resistance Test DefinitionThe winding resistance test of a transformer checks the health of transformer windings and connections by measuring resistance.Purpose of Winding Resistance TestThis test helps in calculating I2R losses, winding temperature, and identifying potential damage or abnormalities.Measurement MethodsFor star connected winding, the resistance shall be measured between the line and neutral terminal.For star connected autotransformers the resistance of the HV side is meas

What is Induced Resistance?InductiveResistance definitionWhen a current passes through the coil, an induced electromagnetic field is formed in the coil, which in turn generates an induced current in the coil to resist the current passing through the coil. Therefore, we call this interaction between the current and the coil electrical reactance.Induced reactance calculation formulaXL= 2πfL=ωLInductive reaction The inductor coil has no hindering effect on DC current, and has hindering effect on AC

What is a Pull-up Resistor?Pull-up resistance definitionA resistor used in an electronic circuit to ensure the known voltage state of a signal.Basic structure of pull-up resistorWorking principleOn the wire to which the pull-up resistor is connected, if the external component is not enabled, the pull-up resistor "weakly" pulls up the input voltage signal. When the external component is not connected, the external "looks" high impedance to the input. At this time, the voltage at the input port ca

What is Light Dependent Resistor?Photoresistor definitionPhotoresistor is a kind of semiconductor device based on internal photoelectric effect, and its resistance value depends on the change of incident light intensity. With the increase of incident light intensity, the resistance value of photoresistor decreases, the incident light weakens, and the resistance value of photoresistor increases. The photoresistor has no polarity, and an external voltage in any direction is applied at both ends wh

What is a Variable Resistor?Variable resistor definitionResistor whose resistance can be adjusted as needed. It is a common component in electronic circuits that allows current or voltage to be adjusted according to Ohm's law.Basic structure of variable resistorA variable resistor usually has three terminals: two fixed terminals at the end of the resistance track and one removable terminal (cursor). Depending on how the terminals are connected to the circuit, a variable resistor can be used as a