Electrical Engineering questions and answers. Measure and calculate the Open Delta voltage unbalance frequently and consider installing a VFD if the unbalance is more than 1 percent in the three-phase circuit. g. This may distort voltage and current measurements, which in turn may influence the protection operation. U 2n = 110 / 3 V. In this the polarity side of A phase is connected to the non-polarity side of C phase. V L = V P V L = V P (1) Figure 1. 73 times greater than, True and more. In Digital Phosphor Oscilloscopes (DPO), the Z-axis can be. The open delta voltage transformer can measure the voltage, current and electric energy of the primary system in conjunction with measuring instruments and metering devices; in conjunction with relay protection and automatic devices, it can form electrical protection and automatic control of various faults in the power grid. Single Phase Power _____ 8. The small signal. This is known as the open delta or V-V delta. 0V LDO) TPS7A3001. . Using a power quality analyzer connected to the drive input, first measure at the input side of the drive. 5VA burden and +/-1. and voltage measurement. These characteristics cause errors in the measurement; refer. Trip logic for philosophy-3. We will focus on the measurement of the voltage vu as indicated in the above circuit. ; 47kΩ = 47 kilo-ohms – which is equal to 47 thousand Ohms. You're describing "high leg" or "wild leg" delta. Question 10. The uncertainty in a measurement, A, is often denoted as (delta)A (read “delta A”), so the measurement result would be recorded as A ± (delta)A. For three-phase applications, two of these units are connected in open-delta (3P3W) and three units are required for wye-wye connections (3P4W). Virtual Instrumentation System to measure voltage, current and power. 1. edu. Δ-connected three-phase voltage sources give greater reliability in the event of winding failure than Y-connected sources. The LibreTexts libraries are Powered by NICE CXone Expert and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University. In this case the angle between the voltage and the current is zero so the power factor ( = cos (angle)) is unity. A transformer that is 1,000 V nominal or less may be located on walls, columns, or structures in the open and does not require ready access. The PTs are magnetically isolated, and each PT input has a nominal voltage of 115 V RMS. Don't know what the OP is asking. The relay most likely uses whatever is connected to Va-Vn as its reference. A differential input is balanced because the gains and. The connectors of this amplifier are always insulated safety banana jacks (red/black). As a temporary measure, when one transformer of a delta-delta bank is damaged and removed for maintenance. rsd =U. To make the transformer connections compatible with three-phase supplies we need to connect them together in a particular way to form a. The difference between two points called as potential difference or voltage drop. rsd =0 L1 L2 L3 Open delta winding for ground fault. In a true ungrounded delta system, a voltage to ground can actually be measured. 57. Find step-by-step Engineering solutions and your answer to the following textbook question: An open-delta three-phase transformer system has one transformer center-tapped to provide a neutral for single-phase voltages. 13(A). Even though the voltage transformers are connected line to ground, it is recommended that the transformers’ primary side have a voltage rating at least equal to the system’s line to line voltage. The capacity of open-delta system = √3 × Rating of one transformer = 0. It used this single L-N nomenclature except they are actually L-L. This solution eliminates the need for the CT which. 071 Spring 2006. The board has eight analog measurement inputs in different combinations: current inputs (1/5 . Turn the dial of the multimeter to monitor DC voltage. Remember: "phase" means a coil or capacitor between two lines or between a line and a neutral. Continuing in the three-phase realm, we discuss exactly how easy delta voltages are to figure out. The relationship between SOC and the discharging voltage at different currents can then be obtained, and the initial SOC during the discharging stage can be deduced. , artificial neural network. The meter will provide per-phase voltage, current, power, and energy readings scaled to correspond to the medium-voltage measurements. Any fault involving earth results shift of Neutral voltage. on and measure the voltage across the rheostat. , the power leg has no use electrically & is a by-product of a Delta or open Delta secondary. 0 Unported Licence. ; 1mA = 1 milli-amp – which is equal to one thousandths (1/1000) of an Ampere. We were thinking of using 3 auxiliary transformers connected to the secondary of the PT's. So on A phase to ground you have straight 480V. – 100:√3 V or 110:√3 V according to IEC for star configuration. 09/01/2012. Open manual. 7% of closed delta system) You can better understand the above calculation with the circuit diagram given in. The second secondary core is intended for a residual voltage measurement utilizing open-delta connection on 100:3V (approximately 33. Center-Tapped, Open Delta mutant. The terms line current and phase current follow the same logic: the former referring to current through any one line conductor, and the latter to. 32 kVA. Easy-to-use feeder protection and innovative features like SEL’s Best Choice Ground Directional Element logic and SELogic control equations provide superior protection on utility and industrial power systems. 2KV to 480V delta delta transformer, through the main switch gear breaker, which feeds all the 1600A feeder breakers. 732 H. Voltage unbalance or imbalance is a measurement of the inequality of the phase voltages and is a common problem, particularly with open-delta three-phase power systems. The system you are describing is called a 240/120V 3 phase 4 wire system. Impacts of measurement accuracy, sensor sampling frequency, and missing data on. We have two existing PT's connected in open delta (connected line to line (A with B) and (C with B)) to a transmission line but we need to measure the line to ground voltage of all three phases. Low Reading. Figure 12 – Three-phase, three-wire, 2 wattmeter method. Thus if we have a ∆-∆ transformer, and we re-move one leg of the delta, then we have a V-V transformer (also called an open delta trans-former). The Delta-Wye transformation is an extra technique for transforming certain resistor combinations that cannot be handled by the series and parallel equations. 5: Three-phase Y and Delta Configurations is shared under a GNU Free Documentation. A rule-of-thumb used by many in the industry is that Neutral to ground voltage of 2V or less at the receptacle is okay, while a few volts or more indicates overloading; 5V is seen as the upper limit. Open delta connection, also known as V-V, is achieved by removing two matching windings from the primary and secondary. The high-voltage (HV) test lead is placed on the H1 bushing terminal and the low-voltage (LV) test lead is placed on the H3 bushing terminal. . With a Star Connection, you can use two different voltages as VL and VP are different. On balanced situations, there is no current flow at open- delta circuit. 2 Gate Threshold Voltage ( V GS(TH))Disadvantages: While the line to line voltages will be equal, the line to neutral voltages will have two phases being equal and one phase being 1. The polarity does not matter. Two identical 1-phase transformers connected in open delta will serve a 3-phase motor load of 250 hp. An open delta 2 transformer bank provides only 57% of the capacity. Rated frequency 50 Hz; 60 Hz. 3 Kelvin (Thomson) measuring circuit 39 A 3. Usually, the step-up excitation test voltage is chosen based on the maximum voltage the test instrument can measure safely and accurately in the HV winding. If the voltage from line to center tap is $277 mathrm {~V}$, what is the high-leg voltage?. 9-3 The Open-Delta Connection. An electric current is injected into the ground through two electrodes, and the voltage difference is measured between two other electrodes (Fig. Photo: TestGuy. Nyquist plot of the built RC-circuit obtained by electrochemical impedance spectroscopy. where 120 V is the nominal phase -to-phase secondary voltage: • V A – V N = 120∠30 (ABC), 120∠–30 (ACB) • V B – V N = 0 (ABC and ACB. 73=65,740. The line voltage is the Voltage measured between any two output lines, and the line current is the current flowing in a line. RMS Voltage and RMS Current A trace of instantaneous voltage as obtained with an oscilloscope is of interest and. Voltage transformer with two secondary windings, one Y-connected and one Open delta connected Figure 5. 2,419. 4: A voltmeter is placed in parallel with a resistor to measure the voltage across the resistor. It is the combination of capacitive potential divider & electromagnetic transformer (auxiliary transformer). Potential or Voltage Transformer: The purpose of the Potential Transformer is to provide an isolated secondary voltage that is in-phase and exact proportionate representation of primary voltage. Most 480V power systems are not a Delta configuration because the phase to ground voltage is 480V or above 300V. The normal operation of a current transformer is to measure current. If the sensor is remote and the system uses a. This test is performed on the primary winding of the transformer. 2. subsequent Voltage ADC measurements. All three line-to-line voltages are calculated using three-wire, open delta voltage measurements from the generator and bus PT inputs. The voltage of the delta winding will be 63. The residual voltage of a system is measured by connecting the secondary windings of a VT in ‘broken delta’ as shown in Figure 4. In addition, the H2 bushing terminal (the third bushing terminal of the Delta winding) is grounded. This amplifier is ideal for the direct connection of high voltage signals. X1, X2, and X3) are open-circuited when the three exciting current measurements are performed. Voltage between two Hot Phases = 120V x 2 = 240V (1-Φ). 118 synchrophasors, and is the economical solution for overcurrent protection. The negative sign comes into play as a result of how we've decided to measure the voltage across winding A and winding C. So to display the units or multiples of units for either Resistance, Current or Voltage we would use as an example: 1kV = 1 kilo-volt – which is equal to 1,000 Volts. 56. The utility may be providing an Open-delta or an open-wye on their side, but it is definitely 3-phase. Thus for safety reasons the terminals of a current transformer should. First, the low-voltage 50-V class isn't really a "class" as such but rather a safety rating. The principle for an open delta winding - Voltages at ground fault in a direct grounded system . However, the reference to Vcb is just to denote that the common connection of the open delta PT's is "b". At the open circuit stage, the relationship between the OCV and the SOC is needed. Additionally, sophisticated decision-making algorithms, e. in units of watts. An alternator with a line voltage of 2400 V supplies a delta connected load. Applications of the Open Delta or V-V Connection. Changing the Voltage Measurement Mode in ATPOL II. Note The instantanuse power/voltage/current can be seen on the inverter LCD screen (in case regulatory inspection requires actual measurement) V OCExamples. We know the phase-to-phase voltage is 4,160V. the two between which is the ground tap). The voltmeter switch would have four positions. The most basic method of taking voltage measurements is to count the number of divisions a waveform spans on the oscilloscope’s vertical scale. These are the general setup and may vary and depend on the installation e. Draw the connections on the diagram below to create an Open-Delta to Open-Delta transformer bank using three single phase transformers. The basic design topology of the VFD with a diode bridge, DC bus capacitors and insulated gate bipolar transistor (IGBT) output has proven to be reliable and beneficial from application and financial perspectives. Open Delta with 50KVA center tapped secondary 30ft away and 10KVA 3 spans away, secondary probably only #4. As a rule, this voltage is 1,73 times higher in the case of an earth fault than the phase-earth voltage in the fault-free network - Both together: some protection devices use both the phase-to-phase voltages as well as the voltage. A phase angle meter connected A-phase to B-phase on a Delta source reads 60 deg for voltage. Conceptually, the delta measurement is far more accurate than the single measurement, because the delta measurement cancels the saturation current and all. 3 = 208 V. also referred to as high leg, stinger leg, etc. Basic three-phase power. 400V and “3U0” will then be 1200V. Each impedance is equal to 16 36Ð °ohms. Unbalanced single phase loads can cause voltage fluctuations and additional, uneven transformer heating. The open delta connection uses two single-phase transformers. The purpose of the open-circuit test is to determine the no-load current and losses of the transformer because of which their no-load parameters are determined. measurements of its input impedance, one when terminated in a short and another when terminated in an open, can be. Ex. Returning to our paper example, the measured length of the paper could be expressed as 11. 1 in. It does this by reducing the effects of any small errors present in the winding of either the primary or secondary coils of the transformer. There are three main configurations of electrical power networks as shown in Fig. What is usually used in high impedance grounded systems is broken delta (three transformers). Where: V L is the line-to-line voltage, and V P is the phase-to-neutral voltage. Utilize the transformers on the Three-Phase Transformer Bank and the Resistive Load to connect. Lastly, the "open" phase lies between line 3 and line 2 and although. AFAIK, most utilities will NOT provide an 'open delta' connection for new services, (and furthermore many will not provide new 'delta' 3-wire services of any kind), due to the problems with the 'stinger' phase as described above. Voltage transformers are devices that allow the measurement of voltage in electrical circuits included in the power system. If either side of the PT were wired in a delta, it would cause a 30° voltage phase shift and incorrect readings. Discussion of how the three phases are still produced in an open Delta transformer. Voltage unbalance or imbalance is a measurement of the inequality of the phase voltages and is a common problem, particularly with open-delta three-phase power systems. This is the so-called open delta operation. The meter will provide per-phase voltage, current, power, and energy readings scaled to correspond to the medium-voltage measurements. When the measured current is relatively small, connect the current measurement terminal between the voltage measurement terminal and the load. e. Figure 1 shows a common setup where three incandescent lamps are used to monitor the three phases: If there are no earth faults on the system all three lamps will illuminate at the same brightness. 17. Since 3 phase power is usually used for high power. An open delta system is a three-phase power system in which one phase of the power circuit is not connected. The Osilloscope's Graph. First, the system voltage with respect to ground is fixed by the phase-to-neutral winding voltage. Use line a as the common potential point. Potential Transformers are used for both Protection and Metering purposes. 577 (or 57 . The measurement is similar to IEC 60270, yet the quasi-integration is conducted at a narrow bandwidth of 9 kHz with a tunable center frequency between 10 kHz to 10 MHz. You will notice that the power output. Ground the the center tap of one transformer if one is available. Like voltage, current can be AC or DC. It does this by reducing the effects of any small errors present in the winding of either the primary or secondary coils of the transformer. 3 in. With an open delta PT connection, B-phase is grounded for safety, at least in medium voltage. Note that the kVA rating of an open delta connection is limited to approximately 87% of the sum of the nameplate kVA ratings of the two single-phase transformers. The voltage terminals of the wattmeters are connected phase to phase. The star-delta starter has both advantages and disadvantages. Similarly, the next phase is between line 1 and line 3. These measurements can be treated just as measuring the voltages directly. Figure 1 – Solidly-Grounded Wye System arrangement and voltage relationships. #17. The measurements were conducted in argon-purged 0. 68. Voltage between three Phases = 240V (3-Φ). When connecting three transformers for three-phase use with a delta secondary, a voltage test should be done before closing the secondary. Compared to a grounded-wye arrangement the open-delta PT only requires two. In-Band Voltage Excursions Synchrophasor Measurements Use IEEE C37. or. input from potential transformers in wye, delta or open delta configurations for secondary voltages up to 347 VAC 50/60 Hz per UL or 400 VAC 50/60 Hz per IEC. In the case of a delta connection,. Tests were performed from the HV and tertiary sides to allow comparison. The fourth being "OFF". OR, Capacity of open delta system = 0. The nominal voltage is 240V not 230V (I know old habits dies hard). Free Download Here pdfsdocuments2 com. 2. 2. The analysis can proceed by considering the two voltage dividers formed by resistor pairs R1, R3 and R2, R4. AFAIK, most utilities will NOT provide an 'open delta' connection for new services, (and furthermore many will not provide new 'delta' 3-wire services of any kind), due to the problems with the 'stinger' phase as described above. Below is a diagram of the open delta connection used in medium voltage measuring circuits. Figure 1. 2n. Commonly, for ground detection on an 11 kV circuit, the primary will be connected in wye. (open delta) and serving a delta connected impedance load. Exercise 2 - Three-Phase Power Measurement; Exercise 3 - Phase Sequence; 86364 - Three-Phase Rotating MachinesOpen-circuit voltage is then a measure of the amount of recombination in the device. A Greater Measure of Confidence Keithley Instruments, Inc. You can only measure three voltages, 1-2, 2-3, & 3-1. - May 16, 2021. The isolation is achieved through the use of AMC1304 that incorporates both high voltage isolation as well as the Delta-Sigma Modulator. delivered to the drive. 4 kV autotransformer. 6 Residually connected voltage transformers The three voltages of a balanced system summate to zero, but this is not so when the system is subject to a single-phase earth fault. Location Ann Arbor, Michigan Occupation EE Aug 17, 2018 #17. The torque equation for a negative-sequence voltage polarized directional element is: 32QT V I V I MTA=•• ∠− −∠+22 2 2[]cos()()( ) MTA = angle of maximum operating torque, dependent upon relay designA Delta-connected relay doesn’t see the Wye voltages, so we’ll remove them in Figure 6-9, which is a good representation of what the test-set thinks is happening using Delta voltages and Wye currents. #2. We are Having a 300 MW generator for which the Secondary open delta voltage of 3rd set of PT's is gradually increasing, and the B phase PT is getting blown out, tapping for the 1st and the 2nd set of PT's derived from the same point as that of the 3rd one, secondary voltages of 1st and 2nd PT's are healthy. For. The existing ground on the center tap of the 120/240 Volt transformer will safely ground the delta. neutral wire may be needed for three phase 240V outlets etc. Most people are accustomed to the single. The applied test voltage is raised in steps, 0. When you need to measure higher voltages, the PT reduces the measured voltage to that suitable for the voltmeter. 7%) Summary Open delta transformers are three phase devices, with only two windings on each of the primary and secondary sides. One a typical 120/240 volt single phase transformer, When the two secondary coils are connected together in series inside the tank, the the secondary voltage. A typical open-delta PT connection is shown in Figure 1. Figure 3 shows the HV-to-tertiary turns ratio measurements for a 288. We know the phase-to-phase voltage is 4,160V. The SEL-351A Protection System has built-in Ethernet and IEEE C37. mA = Milliamps. Any fault involving earth results shift of Neutral voltage. 66 KVA. The performance of. 3. Divide this voltage by the resistance of the load to get the current. Exercise 9-3 - The Open-Delta Connection; 30329 - AC/DC Motors and Generators Open manual. In certain conditions, the complete transformer bank is not employed for the construction of a three-phase. When one Line faults to ground, the primaries become open-delta configured with a voltage increase ratio of √3 (e. Responding to Anonymous' query: (1) The 'high-leg' 3-phase system is more properly referred to as a center-tapped (high-leg or red-leg) 4-wire, delta system. Voltage between two Hot Phases = 120V x 2 = 240V (1-Φ). In this other system, we typically take the B Phase and ground it, so when we measure A-C, C-B, or B-A, the result is 240V; A and C to ground will yield a measurement of 240V, as well, but B to ground will be 0V. 173 kVA Select from the following choices Choose the correct. Whether the neutral is used or not there is still a useful voltage measurement using it to see what is happening in the circuit. Chaniotakis and Cory 11 +-R1 R2 R3 R4 Vs AB. Changing the Voltage Measurement Mode in PSM. However, these models are not fully developed to a complete bus admittance matrix form, which can be readily used. The lamps, in effect, create a weak pull to centre. The standard way to measure resistance is to pass a current through the resistor and measure its voltage drop (see Figure 1). Figure 1. Voltages measured on the secondary side of the VT are in-phase with the individual. 0 and 1. The three-wattmeter method requires voltage measurements from line-neutral. 120/240 V 3 phase is a red leg delta system. Feel like buying Chris a coffee? Think of it as SchulerRuler fueler! pq = (√3V LN cos30°) × 2 = 3V LN (equation 9) Thus, the voltage available to the relay for a phase-to-ground fault on the ungrounded system is three times the line-to-neutral normal voltage. With all the three transformers connected in delta, the power delivered to the resistive load is. In the following video we derive the voltage and answer this seeming. User manuals, specification sheets, CAD drawings and more. The intensity or brightness of the display is sometimes called the Z-axis. 5–4 Hz), and theta. Thus, VA Rating of Bank of three Transformers in Delta = 1. Fixtures to hold the material under test (MUT) are available that are based on coaxial probe, coaxial/waveguide transmission line techniques, and parallel. A linear sweeping voltage is defined by the voltage (or potential) being varied linearly at the speed of the scan rate. A 3D model WattNode meter, with the appropriate voltage range, will correctly measure grounded delta services, but the measured voltage and power for the grounded phase will be zero and the status LED will not light, because the voltage is near zero. 8. c. Most voltmeters are self contained and come with scales ranging from 150V to 750V. In a system that typically has a common neutral or ground between source and load, the neutral or ground must be connected to the variable transformer. 38,000x1. This is because a line toVoltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. Open-delta systems often exhibit increased voltage fluctuation as single-phase loads are applied and removed from the sometimes unevenly sized transformers. 577 x rating of closed delta system=0. We also discuss when the two-wattmeter method. 1. 2. We have two existing PT's connected in open delta (connected line to line (A with B) and (C with B)) to a. 6 Interpretation of the measured values 36 3. The equation is: I = Δ V R. 577 x 15 KVA= 8. Note: The standard known resistance R 0 (in Ω) should be the value of the minimum required isolation resistance (in Ω/V) multiplied by the nominal voltage of the tested device plus/minus 20 per cent (in volts). The results can be seen in the following example: If each of the transformers are rated at 50 kVA and the secondary voltages are 240 volts, then the coil current of each transformer is 50,000/240 = 208 A. Not sure if that's the technical name or not. Figure 7 – Delta connection – three phase, three wires. Leverage Watlow's growing toolkit of calculators, equations, reference data and more to help design your thermal system. A/D converters are ratiometric, that is, their result is proportional to the ratio of input voltage to reference voltage. Open delta, also known as corner-grounded or ungrounded delta, is an electrical configuration of a 3-phase system that provides individual phase to ground connections. For 2-wire ohms, the voltage drop. Delta wiring forms an equilateral. The measurement speed of the voltmeter is critical in determin-ing total cycle time; faster voltage measure-ments mean shorter cycle times. In an open delta secondary circuit there is a voltage also during normal running condition due to unbalances in the network. Now you still measure 120 volts from line to neutral from either line, but from line to line where you previously read 208 volts, you now read 120 volts because the phase angle has been changed. Now with V R4 having 4 volts dropped across it, the voltage difference between points C and D will be 4 volts as: C = 8 volts and D = 4 volts. I have a project where the existing pad mounted utility transformer is configured as delta-delta. The utility may be providing an Open-delta or an open-wye on their side, but it is definitely 3-phase. 1) This is a typical delta to wye configuration. 8 kV) connected Phase A to Phase B on one. 74. Image used courtesy of Amna Ahmad. 1. An open Y-∆ connection requires only two phases plus the neutral on the primary side of the bank in order to develop a three-phase voltage at the. In the case of the open delta configuration, by regulating two phases by +/-10% with regulators, the third phase is also regulated by +/-10%. (2) Visualize the delta-connected secondary of a 3-phase. 1. and one for the open delta voltage signal. The instrumentation which is installed in the plants is generally of electronic or digital type which has reduced consumption on the secondary of the measurement transducers, CTs and VTs (in general. zero volts. U. 6% accuracy of up to 7. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. Open Delta is a 3 phase transformer bank using 2 transformers. #1 I have been working with a power meter recently that has the voltage inputs from an "Open Delta" 3-wire PT arrangement. For reliable resistance measurements, the voltmeter must Voltage (V) Time 4. Balance the loads on the transformer windings as follows: 3-phase loads: one-third of the load on each of the phases. g. Potential Transformers are…. Delta-Sigma VDD_2 = 5. More common is critical loads being wired with three single phase transformers in a. Open delta. Sigma-Delta ADCs. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. Open delta is also used in industrial applications to form a delta-delta transformer connection when both the primary and secondary transformers have similar voltage ratings. Issues such as loose internal connections, faulty tap changers, open circuits, and broken conductor strands or crimp connections may be identified with this test. 3 = 208 V. The period values can be calculated with a definable overlap (up to 99%) and for a definable number of periods (up to 4). Cheapest DMMs (in the $10 range) present lower impedances, but 10Mohm is the value everyone expects from mainstream tools. Broken delta provides 3V0 only. 869 kW, 9. The voltage to ground of a high leg or "stinger leg" on a three phase open delta system will be approximately: 208 Which of the following is the symbol for impedance? Open Delta is a wiring technique that uses three different transformers to provide a 3-phase voltage supply from a single-phase power source. Then we would say the length of the paper is 11. Family Handyman. It is the combination of capacitive potential divider & electromagnetic transformer (auxiliary transformer). Since the phase sequence is R → Y → B, therefore, the direction of voltage from R phase towards Y phase is positive (+), and the voltage of R phase is leading by 120°from Y. (The total load carried by open delta system is 57. If an earth fault occurs on one phase the phase lamp will go out and the others will be brighter. is often used in high-impedance grounded systems and U 2n = 110 V in effectively grounded systems. Making differential voltage measurements is another means of reducing noise in analog input signals. Delta Airlines is one of the leading airlines in the. The star point forms a floating neutral. This solution eliminates the need for the CT which. The zero sequence current of. With the power off and the primaries still wye connected, open the delta and reverse the connections for one of the secondaries, but leave the delta open. voltage and current values during this entire discharge/charge process, the OCV–SOC parameters are obtained. Vbc= Ð ° Z 8 j5bc= - V 220 120 Vbc= Ð ° Z 10 j0ca= + What will be the reading of the two wattmeters connected to measure total power. Notice that the dc voltage value is set to the variable “vs” as defined in line 2. Therfore a voltage measurement from A-phase-to-ground is in phase with the primary VAB, and C-phase-to-ground is in phase with VCB. An open Y-∆ connection requires only two phases plus the neutral on the primary side of the bank in order to develop a three-phase voltage at the.