However, a cell’s internal resistance is anything but a single, unvarying value. A cell’s power density, dissipation, efficiency, and state of health (SoH) all depend on its internal resistance. This is the sample of the test results of the knee point calculation.Internal resistance is one of a few key characteristics that define a lithium ion cell’s performance. The Knee point voltage of the CT is the voltage as per step No.5. If the secondary current increase is 50% with an increase in this 10% voltage.
Apply 5-10 % voltage of the knee point voltage to the secondary of the CT by auto-transformer.Note down the knee point voltage of CT ( as per datasheet of the CT).Disconnect the CT from all external connection.Test Set-up: Test Procedure for knee point Voltage calculation of CT : The test procedure is very simple and can be done if the variable voltage source is available. The current transformer of the PS class can be tested for whether or not the CT has the knee point voltage as per the manufacturer specifications.
Point measure rct how to#
How to Check the Knee Point voltage of the CT? If the knee point voltage calculated on the basis of the power network is higher than the specified knee point voltage of CT, then there is a chance of CT saturation during a fault in the power network, and probably the protection relay will not operate. Knee point voltage of the current transformer is īased on the above calculation, check the rated knee point voltage of CT. If the system fault current is 30 KA, CTR-600/5, RCT+RL+RR=0.5 Ohm
RCT = CT Secondary Winding Resistance, in Ohms If = Maximum Fault Current at the location, in Amperes K = Constant, conventionally taken as 2.0 Knee Point Voltage Formula:ĬT Knee Point Voltage can be calculated using the formula R is the total resistance of the secondary of the CT. The CT knee point calculation can simply be done using Ohm’s Law. The Knee Point Voltage has significance when the CT is used for differential or REF protection. The initial point of the graph is known as an ankle point of the magnetization curve of CT. The point K on the below-given graph is the ‘Knee Point’. The Knee point voltage is selected for PS class(Differential protection) CTs at half of the knee point voltage so that the point lies in between the ankle and the knee point of the magnetization curve of the CT. Therefore, both the set of CTs used at the primary and secondary side of the equipment must have the same knee point voltage and the excitation current(Ie) at Vk/2. If there is variation in knee point voltage of CTs, the CT having less knee point voltage(KPV) will get saturated in case of the external fault and the differential protection relay will get tripped with nuisance tripping. The magnetizing characteristics of both LV & HV sides CTs used for differential protection must have the same knee point voltage V k and the same excitation current I e at V k/2. Importance of Knee Point Voltage for PS class CT: The knee point indicates the CT saturation point on the magnetization curve or B-H curve. The knee point is an important parameter for CT selection for a particular electrical installation. CT Magnetization CurveĪbove knee point, the CT gets saturated. Definition of KPV according to IEC : What is the knee point?Īccording to IEC, Knee Point Voltage of a Current Transformer is defined as the voltage at which a 10 % increase in voltage of CT secondary results in a 50 % increase in secondary current.
For voltages greater than the knee point voltage, the magnetizing current increases considerably even for small increments in voltageacross the secondary terminals. The knee point is defined as the voltage at which a 10% increase in applied voltage increases the magnetizing current by 50%.
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