Power Factor of 3 Phase Power Induction motors and capacitors have limited capacity to regulate the system efficiently. While sychronous motors are complex they inherently balance the system stability. AC generators have base excitation for a 1.0 or unity power factor. Increasing the excitation moves the voltage wave either forward or backward relative to the current wave. The proper reference really cannot be explained by words alone as directional viewing is needed. For example is the view from within the generator or it from some external point such as the load ? The Tesla Polyphase system avoids this characteristic as the stators have even order 4 sets of coils on all machine stator, and 2 sets of coils on the rotor. The excitation only needs to make up for the linear losses or resistance drop to ground. As the voltages increases the add excitation force is lowered to zero. In the case of a 3 phase system that value is never zero, and on average represents 2 to 8 percent losses during normal grid operations. During times of stress those losses for 3 phase is much higher. The Tesla Polyphase system failed to succeed in that the manufacturing base did not exist to make it a cost competitively against 3 phases. The measuring tools also did not exist to quantify the performance differences to make a successful. Nikola Tesla and the few on his sode were simply out gunned by the direct current manufacturing base that made DC solutions. The 3 Phase Solution was a easy conversion for those manufacturers of DC coils to convert to production of AC coils. The 3 phase generator has a base DC magnet. The typical 3 phase generator exciter has 8 to 14 poles so that the magnet has has low resistor losses on the induction of current on the primary stator windings. This DC rotor input, and odd number for stator winding coils-sets up the conditions that create a harmonic content. The so called DC and AC component of the power system. Ideally if the 3 phase system is operating at 1.0 or unity power factor the losses are close to zero. That is as if two magnets are mechanically locked without slippage between the generator and load sources. Because of the nature of Tesla systems to not have a DC excited rotor, it maintains sychronous speeds by self reluctance: That being the other sychronous machine is self exciting the rotor circuit of the other machine. Aka sychronous machines. This principle was well understood by 1882, as it was the method of operating the undersea translantic communcations generators. The two machines were separated by 7000 miles and could instantaneously transfer signals by modulating the power factor signaling. The solution used a inner AC communications conductor and a fully rated neutral return. For Phase Power Nikola Telsa analysis include single pole earth return, and single pole neutral return: He added 2 phase and 4 phase solutions. To include 3 phase and a DC rotor, is stupid... Transformer Overcurrent Protection (HV side) Inverse time overcurrent (51) Overcurrent margin Usually 110% of the rated current, considering An additional 10% margin to rated current is more than enough because the probability of the transformer to load beyond 110% is on the lower side. 💡IDMT IEC IEC IEC IEC Time operating Extremely Long Very Normal curve time inverse Multiplier type💡 inverse inverse inverse Time Setting 🔋The TMS should be adjusted in such a way that the time discrimination between the LV side DMT curve and HV side IDMT curve is at least 200ms. 🔋Also, the TMS should be selected so that the HV relay operating time for the Through fault current in 51 functions is below, 2000 ms. current💡 💡Fault 🔋The fault current that flows through the Transformer for an external fault or a fault in downstream. 🔋The TFC reflects the characteristics of the Transformer damage curve. 🔋The maximum TFC withstand capacity of a Transformer is 2 seconds as per IEC 60076-5 2006 🔋The TFC causes electrical and mechanical effects to the transformer depending on the application, where the mechanical effects are not considered for transformer applications with a low incidence of through fault, for example-Industrial and commercial transformers. 🔋But utility transformers experience a high incidence of through fault, so the cumulative electrical and mechanical effects are considered 🔋The effect of TFC depends on the magnitude, duration, and frequency of through fault incidence. 🔋Instantaneous overcurrent (50) For providing a high stage setting on the HV side two parameters should be considered. 👉Fault current 👉Inrush current 🔋The setting should be calculated with reference to maximum TFC and the short circuit margin should be in the range of 125 % - 200 %. 🔋Using 130 % of the TFC is more than enough, but 175 % and above is selected if the transformer has a higher X / R ratio. 🔋The margin is considered because due to a higher X / R ratio the asymmetricity of the through fault current will be high enough to cause mal-operation and the inrush current magnitude depends on the time of the Circuit breaker closing in the sinusoidal waveform, which can also cause mal-operation if the circuit breaker closes at time Zero. 🔋The time delay for 50 protection functions should be selected for the minimum delay present in the relay. Why is power factor always a concern among utilities and industrial customers? What The PF Real is power factor = power is power the Real ratio of Power does useful real power / factor? to apparent Apparent things or power. Power work. Imaginary power is associated with the creation of expanding and collapsing magnetic fields that are inherent to moving real power with electrical current. Imaginary power can be looked at as being a toll a to deliver real power. The higher the power factor, the more real power that is being delivered per the amount of current or apparent power. What is apparent power? Apparent power is the square root sum of the real and imaginary power. Apparent power = ( (real power)^2 + (imaginary power)^2)) ^.5 This arrangement is often represented by something called the power triangle. The hypotenuse is the apparent power. The horizontal leg is the real power and the vertical leg is the imaginary power. Why is having a low power factor bad? A low power factor means that the system is inefficient because more current is being drawn in relation to the amount of real power delivered (the portion that is doing something useful). This extra current that is drawn uses up the current carrying capacity of cables, breakers, transformers, and other devices. For example, if a system is running at 0.5 power factor, it will have current levels that are twice that of a system running near a perfect 1.0 power factor to transfer the same amount of real energy. This might result in devices needing to be oversized. Voltage issues are also caused by this imaginary power needed due to power factors stemming from two separate issues. Drawing more current and the angle of the current to the voltage. The power factor or ratio of real and imaginary power delivered is determined by the angle difference between the voltage and the current. PF or = in cos( English, atan( the cosine imaginary of the power angle of / real power)) the power triangle. From this, you can see that the current that is leading or lagging the voltage by nearly 90 degrees will have a very low power factor and current that is 0 or 180 degrees in phase with the impedance. Remember this because this is important. Systems with poor power factors almost always have lagging power factors or the current is lagging the voltage. The impedance of cables and transformers is inductive and the voltage drop across the inductor will lead the current by 90 degrees. For reactive current that is lagging by 90 degrees from the voltage, the voltage drop across an inductor will be 90 + 90 = 180 degrees out of phase or a voltage drop. Lagging poor power factors will cause additional voltage drops across cables, conductors, and transformers delivering power to the load. Poor lagging power factors can result in using up the current capacity of devices and causing excessive voltage drops. IED - Intelligent Electronic Device # Substation Automation # Intelligent Electronic Device (IED's) - Comprises of (but not limited to) Microprocessor based voltage regulators, protection relays, circuit breaker controllers, etc. with the capability of serial communication with other devices. Electrical interfacing: All possible electrical interfacing is feasible via an Intelligent Electronic Device (IED). Auxiliary power supply: Older protection relays and voltage regulators may not need auxiliary supply, but IED's always require an auxiliary power supply. Most IED's accept an extended range, e.g., 24-250 V DC/110-240 V AC. Analog inputs: Protection relays and voltage regulators are always provided with current and voltage transformer inputs. Besides that, devices may be provided with sensor inputs (e.g., temperature sensors) and/or 4-20 mA inputs. Note that for some IED's rated secondary current (1A or 5A) and frequency (50 or 60 Hz) must be specified before ordering. Note also that the correct phase of the sensing voltages and currents, and the right direction of the currents are important. Digital inputs: Some IED's require potential-free contacts for digital (logic) inputs, while others recognize the positive power supply voltage (source) or negative power supply voltage (sink) as a logical 1. Digital inputs may be commands or as status information. Analog outputs: Some IED's are provided with transducer outputs, e.g., 4-20 mA or 0-10 V. Mostly these outputs are programmable. These outputs can be active type or passive type outputs. The passive type requires external power supply. Digital outputs: Digital outputs can be potential free normally open, normally close or changeover contacts or solid-state contacts. It is important to check switching capability of the output contacts, because differences can be significant. Digital outputs may be commands or status information. Serial communication ports: There are several ports possible for serial communication like RS 485, ethernet (RJ45), optical, etc. IED's are mostly also provided with an RS 232 or USB port for local communication with a laptop or PC. In order to enable interoperation of IED's from different vendors, IEC created the modern IEC 61850 standard. Functionality: The extended functionality of an IED can be separated into the following groups: Protection Control functions and logics Monitoring Metering Serial communication Human Machine Interfacing (HMI): Almost all IED's are equipped with Human-Machine Interface (HMI) software for commissioning and fault diagnosis. Besides that, most IED's are also provided with a keypad and a display, or it's optional. Setting Studies: In the past a commissioning engineer could adjust a relay or a voltage regulator with three screws and a few dip switches or jumpers, but an IED may contain over 1,000 settings. Excellent HMI software could help to overview all settings and keep them under control.
