Understanding Introduction to Power Quality PDF

# Common Problems at the Customer Side ## D. Deficiencies in the Customer's Distribution System - In some instances, the voltage problem is caused by problems on the customer's electrical facilities, such as: 1. Loose connections 2. Undersized, overloaded or overextended conductors 3....

# Common Problems at the Customer Side ## D. Deficiencies in the Customer's Distribution System - In some instances, the voltage problem is caused by problems on the customer's electrical facilities, such as: 1. Loose connections 2. Undersized, overloaded or overextended conductors 3. Unbalanced distribution of single-phase loads - **Solutions at the Customer Side:** 1. Correct the problem(s) and seek the services of an electrical consultant, if necessary. ## B. Power Factor Correction Capacitors - Most industrial and commercial customers install capacitors to improve the power factor of their system. 1. However, capacitors also raise the system’s voltage and could cause overvoltages during light load/off-peak periods when switched-on permanently. - **Solutions at the Customer Side:** - Manually de-energize the capacitors during off-peak periods. - Install a controlling device (voltage or power factor based) that would energize only the needed capacitor units during certain periods of the day. ## A. Voltage Mismatch - Some customer equipment, usually motors, are rated either 220 volts or 440 volts. - The motors can successfully operate in supply voltages of up ±10% of their rating (198V to 242V for 220-volt motors and 396V to 484V for 440-volt motors). - Our 230- and 460- volts supply voltage, meanwhile, could reach 253V and 506V, respectively, which although still within the ERB limits, are already above the operating range of the motors. - **Solutions at the Customer Side:** 1. Install a special transformer or voltage regulator for the equipment. - **Solutions at the Utility Side:** 1. Adjust the tap setting of the source transformer after careful evaluation of the customer's existing supply voltage. ## Voltage Fluctuation - Series of random voltage changes. - The changes normally are between 95% to 105%. - **Typical Solutions:** - Correction of loose connections - Reconductoring - Provision of separate source for the loads causing the problem ## Voltage Swell - **Causes:** - Line-to-ground faults - Switching-on of capacitor bank - Dropping of large loads - **Effects:** - Failure of electronic and computer devices - Shortened equipment life - Unwanted operation in some relays - RMS voltage variation exceeding 1.1 p.u. for less than 1 minute. ## Voltage Sag (Dip) - **Causes:** - Line-to-ground faults - Starting of large loads (such as motors, ACU and arc furnaces) - Loose connections - **Effects:** - Undetermined - **Typical Solutions:** - Increasing the size of conductor and transformers feeding loads with high inrush current. - Reduced-voltage motor starters. - Use of UPS or constant voltage transformers (CVTs) for sensitive electronic loads. - The graph shows a sine wave with a dip in the middle. - RMS voltage variation between 0.1 to 0.9 of the nominal voltage for less than 1 minute. ## Unbalanced Voltage - **Causes:** - Unbalanced secondary load - Loose connections - Loose neutral or insufficient grounding - Non-uniform transformer taps - Large difference in transformer impedances - One-phase out - De-energized capacitor units - Single-phasing of open-wye, open-delta bank - **Effects:** - Overheating of three-phase motors - Shutdown of equipment due to operation of unbalanced voltage (zero-sequence) relay - **Typical Solutions:** - Load balancing - Correction of loose connections - **Sample Computation of Voltage Unbalance** - Given: - Va = 220V, Vb = 230V, Vc = 235V - Required: - % Voltage Unbalance - Solution: - $V_{ave}$ = (220 + 230 + 235) / 3 = 228.33V - Maximum Deviation = 220 - 228.33 = 8.33V - % Unb. = (8.33V / 228.33V) x 100% = 3.65% - **Formula for Computing Voltage Unbalance on Three Phase Systems** - % VOLTAGE UNBALANCE = (Maximum Deviation from the Average) / (Average Voltage) x 100% - Steady state quantity defined as the maximum deviation from the average of the three phase voltages, divided by the average of the three phase voltages, expressed in percent. ## Overvoltage - **Causes:** - High tap-setting of distribution transformer - High primary voltage - Loose or isolated system neutral/grounding - Wrong transformer connection, polarity or tapping - Single-phasing of open-wye, open-delta bank - Refers to a measured voltage having a value greater than the nominal for a period of time greater than 1 minute. ## Undervoltage - **Causes:** - Overextended secondary lines - Undersized/overloaded secondary lines, transformer lead wires or service drop - Loose connections - Overloaded transformer - Poor/loose grounding or cut system neutral - Wrong tapping of dual voltage transformers in wye-wye banks (120/240V instead of 139/277V) - Low transformer tap-setting - **Effects:** - Equipment malfunction - Dropout of motor controllers - Heating losses and speed changes in induction motors - Shutdown of electronic and computer equipment. - Reduced output of capacitor banks - **Typical Solutions:** - Load shifting or load splitting - Reconductoring - Correction of loose connections - Raising of transformer tapping - Upgrading of source transformer - Installation of line capacitors and AVRS - Refers to a measured voltage having a value less than the nominal for a period of time greater than 1 minute. ## Causes of Low Primary Supply Voltage - Loose connections on the primary - Overextended primary lines - Undersized primary conductors - Low substation bus voltage - De-energized substation/line capacitor banks - Disabled or defective OLTC of substation power transformer - Defective substation/line AVRS ## Common Voltage Problems 1. Undervoltage (Low Voltage) 2. Overvoltage (High Voltage) 3. Voltage Unbalance (Imbalance) 4. Voltage Sag (Dip) 5. Voltage Swell 6. Voltage Fluctuation (Flicker) ## Sample Computations of Voltage Variation - **EXAMPLE 1:** - Given: - Vmin = 215V - Solution: - %Var. = ((215-230) / 230) x 100% = -6.52% - **EXAMPLE 2:** - Given: - Vmax = 250V - Solution: - %Var. = ((250 - 230) / 230) x 100% = +8.70% ## Formula for Computing Variation From Nominal Voltage - % VAR. = (Measured/Given Voltage - Nominal Voltage) / (Nominal Voltage) x 100% ## Parameters and Limits - Power quality begins with knowing the characteristics of the distribution utility, its capabilities and limitations. - Customers must take note of the following parameters in determining the appropriate equipment and system design for their facilities. | Parameter | Limit | |-----------------------|----------------------------------------------------------------------------| | Frequency Variations | Frequency shall be 60 Hz, with allowable variation of 59.7 to 60.3 Hz | | Service Voltages | Plus/Minus 10% of RMS Voltage | | | Secondary Nominal Voltages: 230 Volts, 400 Volts, 460 Volts | | | Primary Nominal Voltages: 13.2 kV, 13.8 kV, 34.5 kV, 69 kV, 115 kV | | Voltage THD | Within 5% | | Voltage Unbalance | Within 2.5% | ## Equipment Manufacturers: - Equipment's rating compatibility - Tolerance of equipment on power disturbance ## Utility Concerns: - Origin and cause of power disturbance - Effect of disturbance on its customers and in the electrical system - Minimize occurrence of power disturbances - Provide reliable power quality service within the prescribed limit ## End-user Concerns: - Types of disturbances which may affect equipment operation - Adverse impact of power disturbance on electrical equipment - Over-all impact of power disturbance on plant operation ## Power Quality Issues - Power quality issues may be viewed from three different perspectives: - End-user - Utility - Equipment Manufacturer ## Definition of Power Quality Problem - “Any power problem manifested in voltage, current, or frequency deviation that results in failure or mis-operation of utility or end-user equipment.” ## Electromagnetic Compatibility - “The ability of a device, equipment or system to function satisfactorily in its electromagnetic environment, without inducing intolerable electromagnetic disturbances in anything in that environment.” - Power quality addresses problems that deal with electromagnetic compatibility. ## Definition of Power Quality - The quality of the voltage, including its frequency and the resulting current, that are measured in the Distribution System during normal conditions. ## The Importance of Power Quality - To understand the concept of what specifically becomes a power quality problem. - To have a common understanding of power quality and its attendant terminology. - To establish collaboration among involved parties in dealing with PQ problems. # Introduction to Power Quality - EENG 105 TOPIC 6: - Understanding the Introduction to Power Quality - ENGR. ERNICK R. ROMEN - Faculty, CVSU EE