In the substation, three single-phase transformers are connected in star- star Configuration and supplied three-phase power to consumers. The voltage terminals of the wattmeters are connected phase to phase. has a voltage rating of 480 V. 32 kVA. The observed frequencies are subdivided into various groups: alpha (8–13 Hz), beta (13–30 Hz), delta (0. 2. Where: V L is the line-to-line voltage, and V P is the phase-to-neutral voltage. The lamps, in effect, create a weak pull to centre. 732I ph. Rated frequency 50 Hz; 60 Hz. These are the general setup and may vary and depend on the installation e. Study with Quizlet and memorize flashcards containing terms like equal to the voltage from line to line, 1. Unbalanced single phase loads can cause voltage fluctuations and additional, uneven transformer heating. The capacity of open-delta system = √3 × Rating of one transformer = 0. For 2-wire ohms, the voltage drop. ; 100uF = 100 micro-farads – which is equal to 100. Consider grounding one phase (corner grounding). 1. The voltmeter switch would have four positions. The measurements were conducted in argon-purged 0. To deliver a three-phase supply to the load, an open delta connection transformer uses two single-phase transformers. PΔ = 3VI. All three line-to-line voltages are calculated using three-wire, open delta voltage measurements from the generator and bus PT inputs. A residual voltage of 110 V is obtained in both cases. Turn the dial of the multimeter to monitor DC voltage. Photo: TestGuy. Overlap: 25%, 50%, 75%, 90%, 95%, 99%. Once you have both the current and voltage, multiply them to obtain the power output. Voltage imbalance is the measure of the voltage differences between the phases of a three-phase system. Resistance values will “drift” at first due to the inductance of the transformer,. When connecting three transformers for three-phase use with a delta secondary, a voltage test should be done before closing the secondary. The meter will provide per-phase voltage, current, power, and energy readings scaled to correspond to the medium-voltage measurements. Family Handyman. 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. A standard three-phase power supply in the U. Three-phase power is linked in a delta configuration. can you tell me what is happening verified all in coming voltages they are good . This voltage drops to 460 V due to line losses before being supplied to connected three-phase electrical equipment. Low Reading. Simple Settings. Conceptually, the delta measurement is far more accurate than the single measurement, because the delta measurement cancels the saturation current and all. Electrical Engineering questions and answers. Cheapest DMMs (in the $10 range) present lower impedances, but 10Mohm is the value everyone expects from mainstream tools. The equations are easy to write down, but cumbersome to solve. Therefore, in Delta Connection, the voltage between (any pair of) two lines is equal to the phase voltage of the phase winding which is connected between two lines. 577 (or 57 . A broken delta is used to measure 3Vo (the sum of the delta voltages) for a ground relay. U. Send data to SEL Phasor Data Concentrators like the SEL-3373 Sta-Voltage between High leg and Neutral = 1/2 x 220V x √3 = 208V (1-Φ). The voltage is initially given by Equation ( ef{1. The supply voltage of the transformer is 480/277 V. Lastly, the "open" phase lies between line 3 and line 2 and although. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. Delta-Sigma VDD_2 = 5. Then the. Determine the VA rating of all loads. V A = 3 V L I p h And for the open delta connection: V A = 3 V L I p h Taking the ratio of open delta to closed delta power, gives: 3 V L I p h 3 V L I p h = 0. 2kV through a high voltage switch to a 13. #1 I have been working with a power meter recently that has the voltage inputs from an "Open Delta" 3-wire PT arrangement. 0 Unported Licence. 17. SINUSOIDAL VOLTAGE AND CURRENT. They feature four and eight measurement channels, respectively. Figure 4. Open-delta connection of transformer is shown in figure 1. If you can shut things down see what voltages look like with no load. An open delta connection only has 58% of the capacity of a full set of three. 0. This can be used to simplify resistance measurement. PT-Name Plate. 2. Both the amplitude and the phase angle are calculated for the virtualV 1 and I 1: they are the Positive-sequence of Voltage and Current at the point of fault. cn). It used this single L-N nomenclature except they are actually L-L. 3 V is used so that the maximum solid ground relay voltage would be 3 × 69. Figure 1 Open-delta PT connection In an open-delta PT connection, V A, V B, and V C voltages are connected to the VA RELAY,VB RELAY, and VC RELAY inputs. 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. The capacitors are connected in series at the primary side of the auxiliary transformer. If the loading question 7 is connected in wye, what would be the line voltage and the line current supply in the load? 104. Ground the the center tap of one transformer if one is available. For example, two units can be ganged in a 3-phase open delta. Due to the fact that the PMM-1 does not have a specific preset measurement mode for. A/D converters are ratiometric, that is, their result is proportional to the ratio of input voltage to reference voltage. ; 47kΩ = 47 kilo-ohms – which is equal to 47 thousand Ohms. We know the phase-to-phase voltage is 4,160V. In medium voltage networks, the basic source of zero-sequence voltage measurements is the open delta system of classic voltage transformers (VTs). 7% of the capacity of a complete Δ-Δ circuit of the same transformers. 4kV e. Reduced starting current by 33% of what the direct online starting consumes, meaning it is economical in terms of electricity consumption. (i. We also discuss when the two-wattmeter method. The open delta voltage transformer configuration consists of two (2) double bushing VTs connected as shown in Figure 1. We know the phase-to-phase voltage is 4,160V. A. 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 this type of connection, the line current supplied to the load I L is equal to the phase current in each. LISNs are used to make conducted emissions measurements as well as provide a stable line impedance used to replicate power lines associated with the EUT/DUT. Schweitzer Engineering Laboratories, Inc. Other voltages for open-delta connection can also be supplied based on customer requirement. on and measure the voltage across the rheostat. That’s why, The open delta will only deliver 57. Sigma-delta (Σ-Δ) ADCs offer multiple benefits when designing RTD systems. /2 2. A 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. The open delta configuration provides a simple means of voltage control, especially when more than one starting voltage is required. When you need to measure higher voltages, the PT reduces the measured voltage to that suitable for the voltmeter. If it still measures approximately zero, adjust the rheostat to minimum resistance and measure the 3 secondary line-to-line delta voltages. 7% of the capacity of a complete Δ-Δ circuit of the same transformers. To make the transformer connections compatible with three-phase supplies we need to connect them together in a particular way to form a. This amplifier can measure ranges from 20 V to 2000 V peak directly, with 5 MHz bandwidth and an accuracy of 0. . 50/60/400Hz Vs DC Vs Variable Frequency. Utilize the transformers on the Three-Phase Transformer Bank and the Resistive Load to connect. Sometimes when you are simplifying a resistor network, you get stuck. Next part of this article will discuss three-phase transformers using the open-delta and open-wye connections, where one of the single-phase transformers making up the three. e. Residual Voltage & Open Delta Voltage Measurement. The high-leg delta (also known as the wild-leg, stinger leg, bastard leg, high-leg, orange-leg, red-leg, and dog-leg delta) is a three-phase electrical service connection. The two design simulators are replicas of the 12 kV electricity. So from what I can tell, the following questions should be asked of the electrician: 1. The Osilloscope's Graph. 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. It is as follows: Capacity of open delta system = √3 x rating of one transformer = √3 x 5 KVA= 8. # 5. 1a). L2 L1 L3 Fault condition L2 L1 L3 Healthy condition L1 L2 L3 U. To move the cursors, click and. I have a delta delta transformer , 480 volts primary 230 volts secondary has worked fine until yesterday , have very low voltage on one phase of secondary , 230 volts a phase 230 volts b phase , and about 15 volts on c phase . Briefly explain. Voltage and current both have a peak value of 1. Measure voltages as high as 8 Vac rms. The difference between two points called as potential difference or voltage drop. Voltage between three Phases = 240V (3-Φ). Measuring 3-phase, 3-wire system with 2 voltage channels and 2 current channels (2V2I) Motor drives often use 3-wire outputs which can be accurately measured by using just 2 voltage and 2 current channels on the oscilloscope. For both methods, the test current flows from the input HI terminal, through the resistor being measured. This parameter will be used to sweep the dc value of the voltage at input node A. 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. Feel like buying Chris a coffee? Think of it as SchulerRuler fueler! transformers in this guide are de-signed to transform primary voltages from 5 – 34. Thus for safety reasons the terminals of a current transformer should. Delta transformer balancing. 0 software can quickly and accurately measure and calculate the voltage unbalance supplied to these industry workhorses as part of the routine energized motor tests that take less than 1 minute. Figure 3 shows the HV-to-tertiary turns ratio measurements for a 288. Voltage is the potential difference between two points of a circuit. 5: Three-phase Y and Delta Configurations is shared under a GNU Free Documentation. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. In this configuration, the PT primaries and secondaries are both wired in wye configurations. 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 kV/26. Vab = Voltage across open delta terminal. 2/3/2020 2 Today: Wye and Delta 7 a b c n c n Assumption 1 (Balanced) • Same phase-neutral voltage • Same phase current Assumption 2 (Positive sequence) • Phase b lags phase a • Phase c leads phase aJust as in the closed-delta pattern, the open-delta voltage at the lines is the same as the coil voltages. Since 3 phase power is usually used for high power. 3 shows a typical voltage transformer. So the magnitude of the torques produced will be the same for a given measure of voltage supplied. Three 120V units can be ganged in a wye connection to result in a 240V line-to-line 3-phase assembly(see Figure 2). kixel co. Then we would say the length of the paper is 11. With all the three transformers connected in delta, the power delivered to the resistive load is. Compared to a grounded-wye arrangement the open-delta PT only requires two. Don't know what the OP is asking. Typical coverage 95% Of Stator Winding. The number of turns also gets reduced by 42 % of the number of turns in delta connection. 1 / 4. In star connection, the phase to neutral voltage is about 58 % of the phase to phase or line voltage. -They can be used at substation where only open-delta Voltage Transformers (VTs) are available-Negative-sequence Directional Overcurrent were not widely used with traditional relays. 2 [16, 17]: Interconnected network topology is adopted in HV transmission networks to provide a secure power supply in the event of an outage, as there are multiple paths to transmit electrical power. If the system is floating, refer your voltage measurements to one phase. Electrical power is the product of voltage times current. 73=65,740. This is one of the known problems with an open delta source. Did he bring in the correct 2 phases (i. 2) Because this is 3-phase the difference in phases is 120 degrees. This shift can be detected by measuring the Voltage across Grounding Resistor Or from the generator terminal Open Delta voltage. The scale is then proportioned to read the actual higher voltage being measured. 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. You can give this any name and starting value. can you tell me what is happening verified all in coming voltages they are good . User manuals, specification sheets, CAD drawings and more. As long as these two assumptions hold true, then the magnitude of the line to line voltage is 1. Delta wiring forms an equilateral. on and measure the voltage across the rheostat. rsd =0 L1 L2 L3 Open delta winding for ground fault. The test measurements I took were accurate enough, mostly within 0. 577. 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. Connecting to Line-To-DC (LDC) Converter Accessory. Figure 2. 732 times larger. 4 kV autotransformer. 58. The topics covered in this post are. It does notify the potential energy stored as electrical charge in an electrical supply point. The zero sequence current of. minimum of two watt meters to measure energy in a delta system, whether it be an open or closed system. Terminal 2 – SMU2: Set to Current Bias (VMU) with a test current of 0A. A three-point-delta method provides more accurate resistance measurements in low-voltage applications. You can do that with a two-step process: Step 1. Open delta connection for voltage measurement Advantages of open delta connection in voltage measurement applications Although only two VTs are in the circuit, we will get all three-phase voltages (Vab, Vbc, Vac). Exercise 9-3 - The Open-Delta Connection; 30329 - AC/DC Motors and Generators Open manual. Fifty volts is considered safe for exposure to uninsulated conductors. Make 3 measurements -- AC, BC, and AB between nodes A&C, B&C and A&B. open delta Configuration. An open delta transformer is a three phase transformer that only has two primary and secondary windings, with one side of the delta phase diagram “open”. For protection purposes, accuracy of voltage measurement may be important during fault conditions, as the system voltage might be reduced by the fault to a low value. Thus, the insulation requirement reduces by 42%. 6. A typical open-delta PT connec-tion is shown in Figure 1. In the case of the open delta configuration, by regulating two phases by +/-10% with regulators, the third phase is also regulated by +/-10%. The maximum HT cutoff values for individual CD instruments differ, but they correspond to the maximum. Potential transformer open delta measurements. The power_compensated example uses a Multimeter block to measure the voltage across the secondary winding of a Saturable Transformer block and the currents flowing through two Series RLC Load blocks. 09/01/2012. 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. This shift can be detected by measuring the Voltage across Grounding Resistor Or from the generator terminal Open Delta voltage. Typical Setting: 5% with 1 Sec TD 100 % Stator E/F Protection This is how we can obtain the three different voltages for this system; however, we can also have a corner-tapped Delta configuration. 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. An alternator with a line voltage of 2400 V supplies a delta connected load. The capacitive potential divider is used to divide the high line voltage to reduce it below 10kV. A buck-boost transformer can be wired in an open delta when the load is relatively low to buck the voltage from 240V to 208V. #2. The Delta-Wye transformation is an extra technique for transforming certain resistor combinations that cannot be handled by the series and parallel equations. Measuring Multiple Parallel Conductors. You may see a 5 KVA or a 10 KVA transformer alongside a 25 KVA, 50 KVA or 100 KVA 120/240 Volt transformer serving single phase loads. First, the low-voltage 50-V class isn't really a "class" as such but rather a safety rating. 071 Spring 2006. 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. You can do that with a two-step. So, voltage across the open Delta terminal can be found as. = – (Vbc+Vca) Here Vbc and Vcaare equal in magnitude, say V but 120° displaced. 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). For a Δ-connected three-phase generator, the phase voltage and phase current are the output voltage and current from each coil. Snyder, PE PDH Online | PDH CenterThe open delta configuration is used for small motors, and the wye configuration is used for large machines. 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. This is close enough for my intended use of the device. Connecting the probes without ground lead to the individual phases should be safe (though with limited common-mode rejection ratio), as long as you observe the overvoltage category rating of both the probes and the scope. The Open-Delta SVR configuration has been well-known 1. 7 kV/95. This voltage exists because of coupling capacitance. Thus, for a 1:1 turns ratio, a star-delta connection will provide reduced voltage to the secondary side by a factor of 0. - Measurement at the open delta winding: Here, the displacement voltage is determined directly by the measurement. “A” with a wavy line over it = AC current. 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. Variable frequency drives (VFDs) have been commonly used in industrial and commercial applications for decades. The wye configuration gives a better voltage balance than the open delta configuration. In an open delta with a center-tapped transformer, label the two ends of the center-tapped transformer as L2 and L3 and label the high leg as L1. Open Delta is a 3 phase transformer bank using 2 transformers. They have 3 phase delta 480. The secondary output voltage of the open delta configuration is equal to 1/root (3) of that delta configuration. You can connect any 2-wire 240v loads between any two phases, even across the open side of an open Delta. 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. 4 to 600V) on each primary. Open or closed delta-connected units are interrelated. 3 in. 577 x 15 KVA= 8. plus or minus 0. Ohm’s Law. (open) leg at an angle other than 120 degrees. The floating Vn wire is just to show that the primary is delta only, neutral is not used. 1 M NaOH aqueous solution (Sigma-Aldrich) as electrolyte. 217 volts on high leg would be normal if the other two phases were reading 125ish. Divide this voltage by the resistance of the load to get the current. Connecting the probes without ground lead to the individual phases should be safe (though with limited common-mode rejection ratio), as long as you observe the overvoltage category rating of both the probes and the scope. on and measure the voltage across the rheostat. V A = 3 V L I p h And for the open delta connection: V A = 3 V L I p h Taking the ratio of open delta to closed delta power, gives: 3 V L I p h 3 V L I p h = 0. Calculating Power in Balanced Delta Three Phase Circuits _____ 21 3C1. Issues such as loose internal connections, faulty tap changers, open circuits, and broken conductor strands or crimp connections may be identified with this test. Re: How to measure 3phase 480VAC with oscilloscope. According to the characteristics presented, all the phase voltage and current waveforms are established after connecting the damping resistor, causing the. 30 10ps 10ps 100ns 2. subsequent Voltage ADC measurements. OPEN DELTA-OPEN DELTA Lesson 11_et332b. Usually, the VT ratio of primary V LN: 69. A 20kΩ per volt voltmeter indicated a reading of 250 V on its 300 V scale when used to measure an unknown voltage. Figure 1. The star point forms a floating neutral. Also, recall that phase difference between Line current and Line-Line voltage (phase to phase voltage) is 30°. The EC-cell was kept inside a KB240 climate chamber (Binder) to ensure a controlled temperature of 25 °C during the measurements. At some instant in time, "A" will be at +120 V relative to the center tap, and "B" will be at -120 Volts relative to the center tap. The nominal voltage is 240V not 230V (I know old habits dies hard). The maximum load power that can be supplied will a. So if A-B, B-C and C-A are all 240 volts, then A-N and C-N will both be 120 volts, but B-N will be 208 volts. this is called “line voltage” or “delta wiring”. I might add that normally these 3 transformers would be built as one chunk of steel with 3 sections, one for each phase. The wye voltage transformer configuration consists of three (3) single bushing VTs. You can connect any 2-wire 240v loads between any two phases, even across the open side of an open Delta. These are the general setup and may vary and depend on the installation e. 1. Voltage transformers with two secondary windings, one for connection in Y and the other in broken delta can then. The newest additions to TI’s family of battery monitors and protectors, the BQ76942 (three cells in series [3S], up to 10S) and BQ76952 (3S up to 16S), integrate a 16-/24-bit delta-sigma analog-to-digital converter (ADC), which is multiplexed to measure each individual differential cell voltage, as well as other selected voltages in the. Three phase transformer connection diagram using this method is shown below. Image used courtesy of Amna Ahmad. Accommodate wye-, delta-, or open-delta regulator configurations. A typical example is shown in Figure 3 below. 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. 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. An open delta transformer is a three phase transformer that only has two primary and secondary windings, with one side of the delta phase diagram “open”. 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. 7%) Summary Open delta transformers are three phase devices, with only two windings on each of the primary and secondary sides. The V-V connected transformers are used to supply a combination of large 1-phase and smaller 3. First, the system voltage with respect to ground is fixed by the phase-to-neutral winding voltage. 3 Kelvin (Thomson) measuring circuit 39 A 3. Connect N to B phase. 5 Definitions of voltage, current, resistance. #3. Then, place the two leads of the meter on either side of the load. Feb 13, 2015. 1 in. Also, recall that phase difference between Line current and Line-Line voltage (phase to phase. 11/05/2014 1:07 AM. The three-wattmeter method requires voltage measurements from line-neutral. Trip logic for philosophy-3. 2KV to 480V delta delta transformer, through the main switch gear breaker, which feeds all the 1600A feeder breakers. SIRIUS XHS LV: Highly isolated low voltage analog input. OR, Capacity of open delta system = 0. of the VT, only A and C phase measurements are in-phase. On balanced situations, there is no current flow at open- delta circuit. The Delta Pro supports up to 1600W of solar input from a variety of panel makers due to the wide voltage range (11-150V) it supports. c. 4 kV autotransformer. Open delta- two xformrs, not broken. Whether the neutral is used or not there is still a useful voltage measurement using it to see what is happening in the circuit. At the most basic level, an oscilloscope's graph of an electrical signal shows how the signal changes over time (Figure 2): Figure 2: X, Y, and Z components of a displayed waveform. tinfoil (Electrical) 16 Jan 06 14:30. 66 KVA. c. Changing the Voltage Measurement Mode in ATPOL II. The voltage across open Δ should be zero. 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. 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. I asked them to take voltage readings between phase-phase and phase-ground just to make sure it is an un-grounded delta secondary. The Open Delta Voltage is used to measure the current flow in a circuit and is also used to calculate the resistance of a circuit. Open-Delta Step Voltage Regulator (SVR). Never open circuit the secondary of a current transformer. 577 (or 57 . In a true ungrounded delta system, a voltage to ground can actually be measured. 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. Limits and precautions. In a static electric field, it corresponds to the work needed per unit of charge to move a test charge between the two points. In certain conditions, the complete transformer bank is not employed for the construction of a three-phase. 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. 68. At the open circuit stage, the relationship between the OCV and the SOC is needed. rsd =0 L1 L2 L3 Open delta winding for ground fault. Ratioed currents and delta voltage measurements are all made inside the part, and a voltage result is presented at the output, with a sensitivity of 4mV/°C. e. be identified Sat 17 Mar 2018 04. Ratioed currents and delta voltage measurements are all made inside the part, and a voltage result is presented at the output, with a sensitivity of 4mV/°C. I’m always surprised when an industrial facility uses a 480 3 Phase Delta power system. 2n. Commonly, for ground detection on an 11 kV circuit, the primary will be connected in wye. For example, in a 230V/400V system, the voltage between any of the phase wire and neutral wire is 230V and the voltage between any two phases is 400V. However, Y-connected sources can deliver the same amount of power with less line current than Δ-connected sources. However, a slightly more compli-cated approach is required when dealing with open-delta PTs. R 0 is not required to be precisely this value since the equations are valid for any R 0; however, a Ro value in this range should. 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. Figure 3 shows the HV-to-tertiary turns ratio measurements for a 288. Overcompensation blocking function • Measurement of RMS value of current and voltage • Wide range of voltage measurement • Current input sensitivity • Separated current input • Ease of programming/setting • 6 or. 100 KVA d. In Gatton Substation, grid voltage steps down from 33 Corresponding author Yong Li is with the College of Electrical and Information Engineering, Hunan University, Changsha 410082, China (e-mail: yongli@hnu. The analysis can proceed by considering the two voltage dividers formed by resistor pairs R1, R3 and R2, R4.