A Website on Maintenance of Electrical Systems

As an electrical engineer / electrical technician you will come across this scenario a from time to time. In my case, the transformer has already been installed, and this transformer fed a block of offices and a small fabrication shop. As the company expanded they decided to add a machine shop with a new machinery like  Lathe machine, Milling machine, drill presses, machines for electroplating and the installed transformer could no longer feed the added load. The a new transformer had already been procured before management asked the question of what size of Circuit breaker would be used to protect this new Power Transformer from overload and short circuit. There a lot of factors to be considered when sizing a circuit breaker but the four major ones that should be on your mind are         The ambient temperature of the environment where the breaker is to be installed.       Continuous running current when all connected loads are switched on (Maximum load current)         Pre

In the maintenance of electric motors periodic inspection of Insulation levels, vibration levels temperature rise and motor noise are generally considered a good practice. When the noise or vibration levels increase significantly it is an indication that the bearing could need lubrication or a complete replacement. Bearings could be mounted using mechanical methods like pressing but this method poses a significant risk of damage to the bearings. This is why heat is used to expand the bearings so that it could easily slide into the shaft and grip the shaft firmly as it cools. The procedure for using a bearing heater is pretty simple and generic. The appropriate yoke close to the inner diameter of the bearing to be heated is selected. This is important for effective and even heating. Then the bearing is placed in the yoke or over the coil. After this, the required temperature is chosen and the heater is switched on then the temperature starts to rise. How induction heaters work

An insulator is a material that resists the flow of electric current through it. Electric insulation is used to direct electricity along the desired path in a circuit and prevent it from straying down unwanted path causing thereby damage to equipment and injury to personnel.  In theory, all the electric current that flows along a conductive wire reaches its intended destination but in real life, some escapes through the insulation. This is because no insulator is perfect and a certain amount of leakage current would flow through the  insulating material  ( dielectric ). Dielectrics are insulators however in the presence of an electrical field the dielectric material becomes polarized.  Electric Polarization is simply when the positive and negative charges within an insulating material shift in opposite directions in the presence of an electric field.  The positive charges within the dielectric are displaced in the direction of the electric field, and the negative charges are

All motor nameplates are not the same. Each manufacturer would have different items on the nameplate but some of the information on the nameplate are standard as required by NEMA(National Electrical Manufacturers Association) and every motor nameplate would contain this information.  Typically every electric motor nameplate contains The manufacturer name - This information helps to identify who made the motor  Enclosure type  - Written as ENCL informs us of the enclosure type and the cooling method for which the motor was designed. There are many types of motor enclosures, and each is designed for specific applications guided by what location the motor is expected to operate. the most popular one being Totally Enclosed, Fan-Cooled (TEFC) meaning that there is a fan on the motor shaft that cools the motor. Others include (XPRF) for Explosion Proof, (ODP) for open drip proof, (TENV) for Totally Enclosed, Not Ventilated and (TELC) Totally Enclosed Liquid Cooled Volts  - This giv

I  resumed my shift, then proceeded to check my email and read the report of the previous shift. They wrote about a breaker tripping continually, stating that necessary checks have been carried out and they figured the circuit breaker was fault. They also advised to reset the breaker anytime it trips until a replacement is made available.  An hour into my work shift it tripped again and I decided to carry out my own checks then I came to the conclusion that the root cause of the tripping was a short circuit.  Due to Insulation degradation, a short happens intermittently and anytime it happens, the breaker trips. When you  flip the breaker on again  it holds but after a while sufficient current jumps through the cracked insulation to form a conducting path between red phase and yellow phase and it trips.  Enough of the back story, I reported to my boss stating that a short circuit was responsible for the continual tripping and the circuit breaker wasn't faulty then the questi

AC contactors are normally not completely noiseless, there is always a degree humming due to  magnetostriction . Magnetostriction  is the   change in dimension of magnetic materials during magnetization . Although when this humming becomes very audible such that it can easily be described as a chatter it raises some questions in the mind of the electrical technician. What causes a contactor to chatter, what is the effect of chattering on the performance of contactor and what can I do to fix it. Common causes of humming in a magnetic contactor. Coil Voltage According to IEC 60947-4-1 the operational limit of the contactor is between 85 and 110% of the rated coil voltage. You should first measure the voltage at your coil terminals A1 and A2 then compare with the rated coil voltage to ensure that incoming voltage to the coil match coil datasheet rating. Undervoltage can cause your contactor to chatter. A 50/60Hz supply voltage would create a magnetic field with a magnetic pull th

NEMA Code letter     kVA/HP with locked rotor A 0 - 3.14 B 3.15 - 3.54 C 3.55 - 3.99 D 4.00 - 4.49 E 4.50 - 4.99 F 5.0 - 5.59 G 5.6 - 6.29 H 7.1 - 7.99 J 7.1 - 7.99 K 8.0 - 8.99 L 9.00 - 9.99 M 10.0 - 11.19 N 11.20 -12.49 P 12.5 - 13.99 R 14.00 - 15.99 S 16.0 - 17.99 T 18.0 - 19.99 U 20.0 - 22.39 V 22.4 and up With the data above it is possible to measure the In-rush current or locked rotor amps from  the Locked rotor code and Rated HP of the motor. Practically it is possible to do it by mechanically strapping down the rotor, then you press the start button and measure the stator current with your clamp-on ammeter. For this example let us assume a 3-phase 75HP motor designed to operate at 460 V   with NEMA Co

The background story goes like this. Our gas turbine has an output rating of 11,000 volts but we had a problem with the Automatic Voltage Regulator (AVR) and it had to be replaced. After replacement, the HMI indicated that the output voltage was 11,000V but the actual voltage on the bus was about 10,400V and this had a ripple effect on the whole system as the output of our 3.3kV transformer was 3.1kV and the output of the 440v transformer was 400v.   After a while, the thermal overload relays on the well-pump motors began to trip one after the other. This prompted us to troubleshoot, and we discovered that the supply voltage to the motor was below the nameplate rating.   Why would a low supply voltage trip the thermal-overload protection relay, normally a when a motor is overloaded it draws more current from the supply and when the motor tries to pull current higher than its full load amperage (FLA) rating the overload opens the circuit to prevent the motor from damage due to o