Bibliotek

High power test and diagnostics combination for medium voltage cables.

This article describes the application of DFR and HV DFR as a preventive method to evaluate the condition and prioritize maintenance activities on HV and EHV bushings and relates some case studies. 

Guide to Low Voltage Motor Testing

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 10.0px Times} span.s1 {font: 10.0px Helvetica} Eftersom en helt perfekt isolation inte är möjlig kommer viss ström att flyta till jord från en ledare som har en högre potential än jord.

Measuring the DC conductor resistance of a rotating machine stator can reveal a lot of information about the machine. It is always desirable to find out the existence of any resistance that is higher than the nameplate value which might be caused by poor joints, corrosion or mechanical deformation of the stator winding.

REQUIREMENTS FOR SAFE WORK ENVIRONMENT WHEN PERFORMING MV or LV POWER CABLE FAULT LOCATING BY DISCHARGING A HIGH VOLTAGE CAPACITOR.

Since the 1950’s vacuum has been used as insulation media in switchgears. Even though that technology has proven to be very reliable, over time air will leak into the vacuum chamber and degrade the insulation. Also, a good practice is to measure after transport or accidents. The accepted way to test the vacuum integrity has always been through a voltage withstand test. For field tests DC test is preferred due to the weight andsize of the instruments.

The is capable of performing turns ratio tests on any phase shifting transformer by allow-ing for phase shifts to be entered with respect to the secondary winding. But with all of the differ-ent ways phase shift is expressed, how do you know if the entered phase shift value is correct?

Power swing which is principally caused by an oscillation in active and reactive power of transmission line, consequent to an enormous disruption in power system, which if not blocked, could cause wrong operation to the distance relay which may lead to tripping the healthy part of the transmission line. In the absence of power swing function it may result in severe damage to the machines or cascading tripping in the grid resulting in blackouts. To prevent such scenarios, intelligent electronic devices (IEDs) have power swing block (PSB) detection and trip logics incorporated with distance schemes. 

Rate Of Change Of Frequency (ROCOF) protection is used in distributed or embedded generation schemes, where a local generator is connected directly to the distribution network, as specified in national standards such as Ansi 81R or G59/3