Effects of unbalanced Electrical Load (Part:2)

EFFECTS OF UNBALANCED ELECTRICAL LOAD (PART:2)

HARMONICS IN SYSTEM BY UPS:
UPS or inverter supplies also perform with poor efficiency and inject more harmonic currents in case of unbalances in the system
DECREASE LIFE CYCLE OF EQUIPMENT:
Unbalanced Voltage increase I2R Losses which increase Temperature. High temperatures, exceeding the rated value of a device, will directly decrease the life cycle of the device and speed up the replacement cycle for the device, and significantly increase the costs of operation and maintenance.
RELAY MALFUNCTION
Unbalanced Voltage flows Negative and Unbalanced Voltage of Voltage or Current. * The high zero-sequence current in consequence of voltage imbalance may bring about malfunctions of relay operation or make the ground relay less sensitive. That may result in serious safety problems in the system.
INACCURATE MEASUREMENT
Negative and zero-sequence components of voltages or currents will give rise to inaccurate measurements in many kinds of meters. * The imprecise measured values might affect the suitability of settings and coordination of relay protection systems and the correctness of decisions by some automated functions of the system.
DECREASE CAPACITY OF TRANSFORMERS, CABLES AND LINES
The capacity of transformers, cables and lines is reduced due to negative sequence components. The operational limit is determined by the RMS rating of the total current, due to ‘useless’ non-direct sequence currents the capacity of equipment is decrease.
INCREASE DISTRIBUTION LOSSES
Distribution network losses can vary significantly depending on the load unbalance. * Unbalance load increase I2R Losses of distribution Lines.
INCREASE ENERGY BILL BY INCREASING MAXIMUM DEMAND
Unbalanced Load increase maximum Demand of Electrical supply which is significantly effects on energy bill. By load balancing we can reduce energy bill. * For Energy Consumption Energy Supply Company does not charge on kVA but on kW for Residential customers. This means that they are charged for the “actual” energy used and not charged for the “total” energy supplied. Thus the power factor and Maximum Demand do not impact residential customers. * But Commercial, Industrial and H.T Connection charged by its maximum demand . We have to specify the maximum “demand“(in kVA) at the time of connection. During the month if you exceed your maximum “demand” you have to pay penalty (or extra price) for the same. That is the MDI penalty that appears on electricity bills. * Let’s assume That Two Company has same approved load of 40 KW and runs 30KW for 100 hours. * Electricity charge = 65 Rs per kWh * Demand charge = 210Rs per kW * Example 1: Company A runs a 30 KW loads continuously for 100 hours but It’s Maximum Demand is 50KW * 30 KW x 100 hours = 3,000 KWh * Energy Consumption Charge =3000×65=195000Rs * Demand difference = 50 KW-40KW=10KW * Demand Charges = 10X210=2100Rs * Total Bill: 195000+2100=197100Rs * Example 2: Company A runs a 30 KW loads continuously for 100 hours but It’s Maximum Demand is 40W * 30 KW x 100 hours = 3,000 KWh * Energy Consumption Charge =3000×65=195000Rs * Demand difference = 40 KW-40KW=0KW * Demand Charges = 0X210=00Rs * Total Bill: 195000+0=195000Rs
FAILURE OF TRANSFORMER
Three-phase voltage with high unbalanced may cause the flux inside the transformer core to be asymmetrical. * This asymmetrical flux will cause extra core loss, raise the winding temperature and may even cause transformer failure in a severe case. * Ideally any distribution transformer gives best performance at 50% loading and every electrical distribution system is designed for it. But in case of unbalance the loading goes over 50% as the equipments draw more current. * The efficiency of transformer under different loading conditions * Full Load- 98.1% * Half Load- 98.64% * Unbalanced loads- 96.5% * For a distribution transformer of 200KVA rating, the eddy currents accounts for 200W but in case of 5% voltage unbalance they can rise up to 720W.
BAD / LOOSE CONNECTION OF NEUTRAL WIRE
In balance Load condition Bad connection of Neutral wire does not make more impact on distribution System but in unbalance load condition such type of Bad neutral connection make worse impact on distribution. * The Three Phase power supplies a small a three-floor building. Each floor of this three-floor building is serviced by a single-phase feeder with a different phase. That is the first, second and third floor are serviced by phase R, Y and B. The external lighting load is connected only on R Phase. * The supply transformer is rated at 150 kVA and connected delta-grounded wye to provide for 430/220 V three-phase four-wire service. * This Transformer has a loose or Bad Neutral connection with the earth. * The transformer delivers a load of 35 kVA at 220 V with 0.9 power factor la…