127 results about "Phase selection" patented technology

A circuit includes a phase selector to generate an injection clock signal having an injection phase based on a phase of a digitally controlled oscillator clock signal generated within a phase-locking feedback loop. An injection-locked oscillator (ILO), coupled to an output of the phase selector, generates an ILO clock signal that is convertible to provide a feedback clock signal of the circuit. Logic, coupled between an output of the ILO and the phase selector, to, at each predetermined number of cycles of the DCO clock signal, cause the phase selector to output a phase shift in the injection clock signal that causes the ILO clock signal to comprise a rotated phase, relative to the injection phase, and that prevents a glitch in the injection clock signal.

The invention provides a resonant grounding system high-resistance grounding fault phase selection method based on frequency domain energy change, and belongs to the field of medium-voltage power distribution network fault detection. The invention provides a phase selection method based on frequency domain energy change in order to solve the problems that high-resistance grounding fault phase selection is difficult and power grid parameters are unbalanced in a resonant grounding system. The method comprises the following steps: firstly, acquiring a three-phase voltage signal of a fault line, and filtering the signal through a 4-order Butterworth low-pass filter to eliminate high-frequency noise interference; analyzing frequency domain energy change of the three-phase voltage before and after the fault by using fast Fourier transform, and extracting fault features; and finally, constructing a novel phase selection criterion based on the positive and negative values of the three-phase voltage frequency domain energy change, the frequency domain energy change vector and the projection thereof, and realizing fault phase selection. According to the method, the fault phase and the non-fault phase can be effectively distinguished, the method is particularly suitable for accurate phase selection of the high-resistance grounding fault, and the reliability and the safety of medium-voltage power distribution network fault diagnosis can be remarkably improved.

The invention discloses a phase selection switch which has multiple phases, each phase comprises a vacuum arc-extinguishing chamber, a magnetic control mechanism and a transmission mechanism, the vacuum arc-extinguishing chamber comprises a moving contact and a static contact, the magnetic control mechanism comprises a moving iron core and a static iron core, and the transmission mechanism comprises a connecting rod assembly, an opening spring and an overtravel spring; the first end of the connecting rod assembly is rigidly connected with the moving contact, the second end of the connecting rod assembly is connected with the moving iron core in a follow-up mode, the second end of the connecting rod assembly penetrates through the static iron core and the moving iron core, and the opening spring and the overtravel spring are both arranged in the middle section of the connecting rod assembly. The beneficial effects of the invention are that the connecting rod assembly passes through the magnetic control mechanism, so that the over-travel distance is formed between the connecting rod assembly and the magnetic control mechanism, the over-travel value of the contact over-travel spring after leaving a factory can be observed and measured, and the wear condition of the vacuum arc-extinguishing chamber contact in the phase selection switch can be conveniently found in time in the later stage.

The invention relates to the technical field of industrial big data, and discloses a phase selection circuit breaker intelligent control method and system based on big data, and the method comprises the steps: collecting the original operation data of each node, extracting the load peak valley, voltage fluctuation and current instability characteristics, completing the state evaluation, and generating an initial operation data set; carrying out standardization, denoising and seasonal leveling treatment to obtain a cleaned load feature set; fusing the frequency deviation and the power factor change, executing trend operation, and forming a load trend prediction data set; in combination with real-time voltage fluctuation and a temperature coefficient, load response characteristics are analyzed, and a preliminary control opportunity adjustment scheme is determined; the current instability index and the harmonic interference intensity are corrected based on the scheme, and an operation parameter combination is formed; finally, according to the parameter combination, a control instruction is generated, time sequence scheduling is completed, and a control execution plan is output. The method can solve the problem of response lag of the circuit breaker under complex working conditions.

The invention relates to the technical field of electric power, in particular to a vacuum circuit breaker and a phase selection closing control method, and the vacuum circuit breaker comprises a hybrid electromagnetic mechanism and a vacuum arc-extinguishing chamber; the hybrid electromagnetic mechanism comprises a permanent magnet closing assembly and an electromagnetic repulsion opening assembly, the permanent magnet closing assembly comprises double coils and a T-shaped movable iron core which are arranged in parallel, and a discharge loop is formed to drive a movable contact of the vacuum arc-extinguishing chamber to complete a closing action and maintain a closing state; the electromagnetic repulsion opening assembly comprises a static coil panel and a moving coil panel which are coaxially and oppositely arranged to form a reverse current repulsion loop so as to drive a moving contact of the vacuum arc-extinguishing chamber to complete an opening action and maintain an opening state, and the moving coil panel is connected with a T-shaped moving iron core of the permanent magnet closing assembly through an insulating guide rod; the vacuum arc-extinguishing chamber comprises a driving connecting rod, a moving contact and a static contact, one end of the driving connecting rod is connected with the moving contact, and the other end of the driving connecting rod is connected with the insulating guide rod. Therefore, the opening and closing speed of the vacuum circuit breaker is improved.

According to the multi-phase clock self-calibration circuit provided by the invention, detection quantization and calibration of phase deviation are realized by utilizing the phase detection circuit, the digital time converter, the phase selection circuit, the phase detection circuit and the digital control circuit, and the phase detection circuit is high in detection precision; according to the invention, the phase detection circuit is simple in structure and low in cost, the sub-picosecond phase calibration can be realized by adopting the relative phase deviation quantization technology, and the phase detection circuit is insensitive to the change of process, temperature and voltage deviation by adopting the differential technology, so that the quantization error caused by the phase detection circuit is remarkably reduced, and the high-precision calibration of the multi-phase clock signal is further realized.

The invention provides a double-end weak feedback AC system model identification phase selection method and system based on harmonic injection, and the method comprises the steps: collecting the amplitude information of negative sequence current and positive sequence voltage at a protection installation part of a new energy side, and achieving the switching of harmonic injection modes through employing the amplitude information as a starting criterion; on the basis of harmonic injection, an equivalent model of a fault phase and a non-fault phase of the double-end weak feed alternating current system under specific harmonic waves is constructed, and a criterion is constructed by using the difference of the model so as to judge the fault phase; and after a fault occurs, judging harmonic current and voltage amplitude signals of each phase collected at the protection installation position of the new energy side of the line by utilizing a protection criterion, and judging whether the phase is a fault phase or not.

The invention discloses a control strategy fusion verification method for a circuit breaker phase selection device, and the method comprises the steps: verifying the performance and control strategy of the circuit breaker phase selection device, measuring the offset # imgabs0 # of an input signal of a sensor, carrying out the preset working condition simulation and characteristic parameter setting of the phase selection device, inputting a switching-off / switching-on command to the phase selection device, and carrying out the verification of the performance and control strategy of the circuit breaker phase selection device. The phase selection output signal of the phase selection device is monitored to reversely deduce the delay time # imgabs1 # calculated by the phase selection output signal, and the offset # imgabs4 # between the actual delay time # imgabs2 # and the standard delay time # imgabs3 # is obtained; based on no-load verification and electrified verification, fusion verification of linkage of a circuit breaker phase selection device and a circuit breaker is carried out, an output signal of the phase selection device and action data of the circuit breaker are collected, and the offset of an actual closing / breaking phase and a target closing / breaking phase is obtained; and evaluating the performance, the strategy and the phase selection effect of the phase selection device based on the offset # imgabs5 # and the offset # imgabs6 # of the input signal of the sensor and the offset of the actual closing / opening phase.

An active transmission type intelligent metasurface and a matching circuit applied to the intelligent metasurface, the circuit comprising: a receiving antenna for receiving an electromagnetic wave signal; a power amplification unit for amplifying the electromagnetic wave signal received by the receiving antenna; a phase coupling unit for modulating the amplified electromagnetic wave signal into electromagnetic wave signals with various phase differences; a phase selection unit for selecting an electromagnetic wave signal with a required phase difference from the electromagnetic wave signals with various phase differences; and a radiation antenna for radiating the electromagnetic wave signal with the corresponding phase difference; the intelligent metasurface comprises a plurality of active transmission intelligent metasurface units arranged periodically to form an N*M array, and each active transmission intelligent metasurface unit in the array comprises an active transmission circuit. The present application realizes the active amplification function which the existing transmission RIS structure does not have and has the 2-bit phase control function, and the present application has low design complexity, low deployment cost and good system performance.

The present application relates to the technical field of electrified railway control, and discloses a phase control closing method and a heavy haul locomotive circuit breaker, the method comprising: step one, establishing equivalent mathematical models for the heavy haul locomotive, traction substation, AT substation and traction network; step two, establishing a vehicle-network-station simulation model based on a MATALB / Simulink simulation platform; step three, obtaining the influence of different line loads on phase selection closing according to the vehicle-network-station simulation model; and step four, determining a phase control closing scheme and conducting test verification. The phase control closing and opening method of the heavy haul locomotive circuit breaker with the above structure can establish equivalent mathematical models for the heavy haul locomotive, traction substation, AT substation and traction network, and then establish a vehicle-network-station simulation model, analyze the influence of different line loads on phase selection closing, and determine a phase selection closing scheme according to the breakdown characteristics of the circuit breaker and the analysis results. The phase selection closing scheme determined through test verification can achieve the purpose of reducing the overvoltage of the closing system.

The application discloses a transformer on-load tap changer based on a phase selection technology and a gear switching method, which comprises a main circuit and a transition circuit connected with transformer winding taps, the main circuit comprises gear selection circuit and on-off circuit connected in sequence, the gear selection circuit comprises at least four relays for switching the working gear of the transformer; the on-off circuit is composed of vacuum circuit breaker VCB2, diode D2 and vacuum circuit breaker VCB4 connected in series; the transition circuit is formed by transition resistor R, vacuum circuit breaker VCB1 and diode D1 connected in parallel, and vacuum circuit breaker VCB3 connected in sequence, the transition circuit cooperates with the main circuit to realize the arcless switching of the transformer gear; all the vacuum circuit breakers are controlled to act by permanent magnet operating mechanisms, and the permanent magnet operating mechanisms are used to drive the vacuum circuit breakers to realize the fast on-off according to the voltage phase signal. The application controls the action of the vacuum circuit breaker by the phase selection technology and the conduction and cutoff characteristics of the diode, reduces the generation of arc, and prolongs the electric life.

The invention discloses a large-view-field polarization detection super lens based on an instrument matrix, and relates to the technical field of micro-nano optics and polarization detection. Comprising four sub-lens structures. A secondary phase distribution and global optimal phase screening strategy is adopted in the structural design, and a calibration method based on an instrument matrix is provided. According to the structure, different polarization components are spatially separated and focused, and polarization response of a system at different incident angles is accurately calibrated by using an instrument matrix, so that polarization detection in a large view field range of 120 degrees is realized. The invention has the characteristics of super compactness and high precision, and can be used for designing polarization detection, polarization imaging and the like in a large view field range.

The application discloses a phase selector switch operating mechanism, which comprises an operating panel, an isolation operating shaft, a grounding operating shaft, interlocking part one and interlocking part two, the isolation operating shaft and the grounding operating shaft are arranged on the operating panel, the interlocking part one is installed on the isolation operating shaft, the interlocking part two is installed on the grounding operating shaft, and the interlocking part one and the interlocking part two are matched through a limiting structure. The application has the beneficial effects that: through the interlocking part one, the interlocking part two and the limiting structure, when the isolation switch is closed, the interlocking part one matched with the limiting structure can block and lock the grounding operating shaft; when the grounding switch is closed, the interlocking part two matched with the limiting structure can block and lock the isolation operating shaft; and thus, the double locking function is realized, and the safety of the switch equipment is further improved.

This reception circuit includes a clock generation circuit that generates a reception clock signal, and a plurality of data reception circuits that respectively receive separate data signals on the basis of the reception clock signal. The clock generation circuit includes: a variable delay circuit for generating a delay reference clock signal by delaying, by a delay amount corresponding to a delay control signal, a reference clock signal received by a clock reception circuit; a delay synchronization circuit for sequentially delaying the delay reference clock signal to generate a plurality of internal clock signals; and a selector circuit for selecting one of the plurality of internal clock signals on the basis of a phase selection signal and outputting the selected one as a reception clock signal. Thus, it is possible to generate a clock signal capable of receiving a plurality of data signals at an appropriate timing while suppressing an increase in power consumption.

A phase selector / phase interpolator circuit which includes two phase selector circuits and one phase interpolator circuit, each phase selector circuit includes N first tail current tubes, N phase selector units, a current source circuit and a comparison circuit. The current source circuit is selected as a load of the phase selector circuit. The comparison circuit compares a common-mode voltage of the two output clock signals output from the phase selector unit with a reference voltage, and performs negative feedback regulation on the first bias voltage of the first tail current tubes, so that the common-mode voltage can be controlled to be equal to the reference voltage, a tail current of the first tail current tubes is controlled to be equal to the current of the current source circuit, and the output waveform becomes a linear triangular wave.

The invention discloses a phase rotator in a spread spectrum clock generator and the spread spectrum clock generator, relates to the technical field of clock spread spectrum, and aims to solve the problems that the phase rotator of the spread spectrum clock generator in the prior art is not suitable for high-frequency signals and is high in power consumption. The phase rotator comprises a coarse adjustment loop and a fine adjustment loop. The coarse adjustment loop is connected with the fine adjustment loop; the coarse tuning loop is used for performing first phase segmentation on an input high-frequency differential clock signal to obtain multiple paths of modulation phase signals, and selecting a target single-path modulation phase signal from the multiple paths of modulation phase signals based on a phase selection signal; and the fine adjustment loop is used for performing second phase segmentation on the target single-path modulation phase signal to obtain multiple paths of high-resolution phase signals, and selecting the target single-path high-resolution phase signal from the multiple paths of high-resolution phase signals based on the phase selection signal. The invention is used for realizing the processing of the clock spread spectrum generator on the high-frequency clock signal and reducing the power consumption.

The invention relates to a large-scale wind power plant sending-out line phase selection method based on transient current waveform characteristics, and belongs to the technical field of power system relay protection. Firstly, transient current of a wind power plant side is collected, and whether a fault is a grounding fault is judged according to the magnitude of zero-mode current; if the fault is a ground fault, absolute values of integral value ratios of transient current fault components of all phases and 1 difference values are calculated, judgment is carried out according to a ratio corresponding to the minimum value delta kmin in the absolute values, if the ratio is smaller than the other two ratios, the fault phase is one phase except the two corresponding phases in the ratios, and if the ratio is larger than the other two values, the fault phase is one phase except the two corresponding phases in the ratios. The fault phase is the corresponding two phases in the ratio; if the fault is a two-phase short-circuit fault or a three-phase short-circuit fault, the ratio of the integral value corresponding to the delta kmin is judged, if the ratio is larger than the other two ratios, the fault is the two-phase short-circuit fault, and otherwise, the fault is the three-phase short-circuit fault. According to the method, the required time window is short, and the problem that fault phase selection is inaccurate when a traditional phase selection method is used for recognizing far-end high resistance is solved.

The application discloses a phase selection circuit of a multiphase control circuit and the multiphase control circuit, which comprises an amplifier circuit, a comparator circuit, a clamping state control circuit and a clamping signal control circuit. The amplifier circuit is configured to generate a comparison signal. The comparator circuit is configured to generate a phase switching signal according to the comparison signal and a second reference voltage signal. The clamping state control circuit is configured to generate a clamping state control signal and provide the clamping state control signal to the clamping signal control circuit. The clamping signal control circuit is configured to clamp the voltage value of a clamping signal at a clamping reference voltage. By setting the clamping state control circuit and the clamping signal control circuit for the multiphase control circuit, the inductance current peak value of the multiphase control circuit is clamped when the phase switching is performed during the load switching of the multiphase control circuit, so that the problem that the output voltage signal oscillates during the light and heavy load switching of the multiphase circuit in the prior art is solved.

The application discloses a phase selector switch, which has multiple phases, each phase comprising a vacuum interrupter, a magnetic control mechanism and a transmission mechanism, the vacuum interrupter comprising a moving contact and a stationary contact, the magnetic control mechanism comprising a moving iron core and a stationary iron core, and the transmission mechanism comprising a connecting rod assembly, a breaking spring and an overtravel spring; the first end of the connecting rod assembly is rigidly connected to the moving contact, the second end of the connecting rod assembly is connected to the moving iron core in a follow-up mode, and the second end of the connecting rod assembly passes through the stationary iron core and the moving iron core, and the breaking spring and the overtravel spring are arranged in the middle section of the connecting rod assembly. The application has the beneficial effect that the connecting rod assembly passes through the magnetic control mechanism, so that an overtravel distance is formed between the connecting rod assembly and the magnetic control mechanism, and the overtravel value of the contact overtravel spring after the factory delivery can be observed and measured, and the wear condition of the vacuum interrupter contact in the phase selector switch can be found in time in the later period.

The embodiment of the invention provides communication equipment and a data processing method, relates to the technical field of chips, and improves the performance of the communication equipment. According to the specific scheme, the communication equipment comprises a receiving module, a sending module, an interference canceller and a phase selector. When the communication device is in a first state, the receiving module is used for sampling a received first signal based on N sampling phases to obtain N first input signals, the N sampling phases and the N filtering coefficients are in one-to-one correspondence, and N is an integer greater than or equal to 2. The interference eliminator is used for filtering the second signals sent by the sending module based on the N filtering coefficients to obtain N filtered second signals. The phase selector is used for obtaining N signal attenuation values based on the N first input signals and the N filtered second signals. And the phase selector is also used for determining the filtering coefficient corresponding to the minimum signal attenuation value in the N signal attenuation values as a target filtering coefficient.

A multiphase switching voltage regulator is disclosed. The regulator includes a first clock generator circuit configured to receive a reference clock, and to generate M first clocks, where the M first clocks are phase separated by 360° / M, a plurality of phase extrapolator circuits, where the plurality of phase extrapolator circuits includes N phase extrapolator circuits, and a phase selector multiplexer configured to provide one of the M first clocks to each of the phase extrapolator circuits, where the N phase extrapolator circuits are configured to generate N output clocks, where the N output clocks are phase separated by 360° / N.

The present disclosure relates to a method for determining a fault type of a fault on a transmission line, wherein the transmission line is comprised in an electrical system, the method comprising: obtaining a sequence voltage and / or current determined for a first location on the transmission line and a further at least one voltage and / or current determined for the first location on the transmission line; and determining the fault type of the fault on the transmission line by evaluating a plurality of criteria involving the sequence voltage and / or current and the further at least one voltage and / or current.

The invention relates to a single-phase outgoing line power distribution cabinet capable of realizing inter-phase balance, which comprises a box body, a voltage collector, a phase selection switch, a UPS (Uninterrupted Power Supply) power supply unit, a phase angle measurer and a control unit, the phase selection switch comprises a shell, a switching bus and a driving assembly, terminals of live wires of all phases are evenly distributed at the position of the shell along the center line, and the driving assembly drives the switching bus to enable the terminals at the position of the switching bus to be communicated with the terminals of the live wires of the corresponding phases. The UPS power supply unit comprises a power supply and an inverter, and the voltage collector, the phase selection switch, the UPS power supply unit and the phase angle measurer are electrically connected with the control unit. The single-phase outgoing line power distribution cabinet capable of realizing inter-phase balance has the beneficial effects of automatically realizing inter-phase switching and uninterruptible power supply.

The present invention discloses a fractional multi-mode frequency divider circuit based on space-time averaging and phase interpolation technology, comprising: a third-order noise shaping modulation module, a dynamic element matching and phase selection module, a phase switching frequency divider module, and a pipelined phase interpolation module; the third-order noise shaping modulation module is used to perform time averaging on the input frequency division ratio to generate an instantaneous frequency division ratio; the dynamic element matching and phase selection module is used to perform spatial averaging on the instantaneous frequency division ratio and generate a frequency divider control word and a phase interpolator control word; the phase switching frequency divider module is used to generate a clock signal corresponding to the frequency division ratio based on the frequency divider control word; and the pipelined phase interpolation module is used to perform phase interpolation on the clock signal to generate a final clock signal with an accurate phase. The embodiments of the present invention utilize the mutual cooperation of the various modules to achieve the integration of space-time averaging technology and phase interpolation technology, thereby improving the limitations of space-time averaging technology.

The invention discloses a multi-phase clock signal output circuit and a control method thereof. The multi-phase clock signal output circuit comprises at least two clock signal output links; and each clock signal output link comprises a phase selection module, a phase conversion module and a delay module. A plurality of input ends of the phase selection module are electrically connected with a plurality of clock signal input ends in a one-to-one correspondence manner, the input end of the phase selection module is used as the input end of an output link of clock signals, and the output end of the phase selection module is electrically connected with the input end of the phase conversion module; and the phase selection module is used for selecting an input clock signal. The output end of the phase conversion module is electrically connected with the input end of the time delay module, the phase conversion module is used for inverting the phase of the clock signal, and the time delay module is used for adjusting the phase of the clock signal. According to the invention, large-range and high-precision clock signal output is realized.

The embodiment of the invention discloses a transmission link control system and a transmission link control method. The system comprises: at least two sending links; wherein any sending link comprises a multi-phase generation circuit and a phase selection circuit of a frequency division clock; the multi-phase generation circuit is used for generating at least two clock sending phases and sending all the clock sending phases to the phase selection circuit; and the phase selection circuit receives all the clock sending phases sent by the multi-phase generation circuit, determines a target phase according to all the clock sending phases, and sends the target phase to the multi-phase generation circuit, so that the multi-phase generation circuit generates a synchronous clock signal according to the target phase. According to the embodiment of the invention, the time sequence deviation skew of the sending modules among different links is effectively and accurately controlled, the algorithm precision is improved, the calibration judgment time is shortened, and a solid foundation is laid for realizing accurate link synchronization and ensuring the correctness of received data.

The invention relates to the technical field of power system relay protection, in particular to a mixed precision quantification method for single-phase earth fault line selection. Comprising the steps of S1, fault line selection data set preparation and basic model training, S2, channel-level quantitative sensitivity evaluation, S3, channel sensitivity grading and prior construction, S4, mixed precision bit width proportion sequential search, S5, bit width distribution based on actor-commentator reinforcement learning, and S6, quantitative perception training and parameter updating. According to the mixed precision quantification method for single-phase earth fault line selection, through the design of unbalanced sample enhancement, channel-level sensitivity evaluation, reinforcement learning bit width distribution, quantification perception training and deployment adaptation verification, the targets that the precision loss of a fault phase selection model is smaller than or equal to 3%, the compression ratio is larger than or equal to 4 times, and the reasoning time is smaller than or equal to 200 ms are achieved; the real-time deployment requirement of the power distribution network edge equipment is met, and the accuracy and timeliness of single-phase earth fault phase selection are improved.

A circuit includes a phase selector to generate an injection clock signal having an injection phase based on a phase of a digitally controlled oscillator clock signal generated within a phase-locking feedback loop. An injection-locked oscillator (ILO), coupled to an output of the phase selector, generates an ILO clock signal that is convertible to provide a feedback clock signal of the circuit. Logic, coupled between an output of the ILO and the phase selector, to, at each predetermined number of cycles of the DCO clock signal, cause the phase selector to output a phase shift in the injection clock signal that causes the ILO clock signal to comprise a rotated phase, relative to the injection phase, and that prevents a glitch in the injection clock signal.

The application discloses a method, medium and system for determining the closing speed of a phase-selected vacuum switch for closing a capacitive load, comprising: repeatedly performing multiple closing experiments on the fast vacuum switch at different closing speeds and at different closing phases under a power frequency voltage; collecting the minimum pre-breakdown voltage and the power frequency voltage corresponding to the closing process of each closing speed; drawing the curve of the minimum pre-breakdown voltage corresponding to each closing speed of the fast vacuum switch changing with time and the curve of the power frequency voltage changing with time; if the closing process corresponding to at least one closing speed meets a first preset requirement, selecting the smallest closing speed as the lower limit of the closing speed of the fast vacuum switch; and the first preset requirement is that the slope of the curve of the minimum pre-breakdown voltage changing with time is greater than the slope of the curve of the power frequency voltage changing with time at the same time. The application determines the minimum closing speed, and reduces the pre-breakdown high-frequency inrush current in the process of closing the capacitive load by the vacuum switch.

The present application relates to the technical field of power system relay protection, and especially to a mixed precision quantization method for single-phase ground fault line selection, comprising the following steps: S1, fault line selection data set preparation and basic model training; S2, channel level sensitivity evaluation; S3, channel sensitivity grading and prior construction; S4, mixed precision bit width proportion sequential search; S5, actor-critic reinforcement learning based bit width allocation; and S6, quantization perception training and parameter updating. The mixed precision quantization method for single-phase ground fault line selection realizes the target of "precision loss ≤ 3%, compression ratio ≥ 4 times, and inference time ≤ 200 ms" of the fault phase selection model through the design of "unbalanced sample enhancement-channel level sensitivity evaluation-reinforcement learning bit width allocation-quantization perception training-deployment adaptation verification", meets the real-time deployment needs of the power distribution network edge device, and improves the accuracy and timeliness of single-phase ground fault phase selection.