Technical Presentations

Switching of Inductive Currents and Dimensioning of RC-Snubbers with PAMSUITE846

Abstract
In order to control the voltage in distribution and transmission networks shunt reactors can be used for compensation of reactive power. Due to the switching of their inductive currents, unacceptable ... see moreswitching transient voltages might occur which can lead to damage of equipment. Furthermore, the breaker must be able to withstand the transient recovery voltage (TRV), amplitude and rate of rise (RRRV) respectively. One possibility to mitigate these switching transients are so-called RC Snubbers. They have to be dimensioned according to the topology and the values of R and C can be optimized with the PAMSUITE tool. In this presentation the modelling and the results of the TRV due to shunt reactor switching is discussed and the mitigation with RC Snubbers with the help of PAMSUITE is shown.

Tag(s): TRV, PAMSUITE, snubber, switching

Analysis and Calculations in Medium Voltage Electrical Systems833

Abstract
The electrical installation of an industrial site is a complex structure. Analyzing behavior in a transient condition allows optimum selection of the operation and protection devices in the installati... see moreon design phase; in addition, possible weaknesses and critical points can be highlighted in advance, allowing prevention of potential problems, damage to machinery, and costly periods of down time.

In order to completely satisfy the needs and expectations of the customer, in ABB Electrification Business an important role is played by analyses and consulting services offered by Field Application Support (FAS) specialist.

In this session of the "EMTP User conference", representatives from the Italian ABB Distribution Solution division, based in Dalmine (BG), will show how EMTP tool supports the analyses performed within the "Medium Voltage Circuit Breaker Suitability" reports that are provided to customers looking for switching devices for special applications. In particular, the today presentation will focus on "CB suitability" study approach for the Generator Circuit Breaker and the Filter Harmonics switching applications

Tag(s): TRV, generator breaker, filter, switching

Impact of Power Transformer Energization on Relay Protection Operation844

Abstract
One of the main causes of the incorrect operation of transformer relay protection are inrush currents. The transient inrush current occurs when energizing the unloaded transformer, and it is a consequ... see moreence of the transformer core saturation. This paper presents analysis of transients caused by energization of 300 MVA three-phase autotransformer with stabilizing winding and voltage ratios 400/115/10,47 kV.

Using the PAMSUITE Toolbox in EMTP, many simulations were performed to show the impact of model’s parameters on the amplitude and duration of inrush currents as well as the probability of 2nd harmonic differential current amplitude occurrence. Simulation results show that controlled switching reduces inrush currents amplitudes and increases 2nd harmonic content in differential currents. A Protection Toolbox in EMTP was used for modelling CT saturation and operation of transformer’s differential protection relay.

Based on the simulation results the optimal differential protection settings were determined, and the probability of false relay protection operation was calculated.

Tag(s): transformer, energization, inrush, differential, protection, harmonics, bctran, pamsuite

Single Pole Auto Reclosure and NGR Analysis 794

Abstract
Unsuccessful auto reclosure has been observed in 765 kV HVAC transmission lines connected with Generation Bus. Back up Impedance Protection of Line reactor triggered during AR dead time due to power f... see morerequency oscillations in faulty phase (disconnected phase). It triggered tripping of Non Switchable Line Reactor at one end, which resulted tripping of 765 kV HVAC Line and avoidable Generation loss.

These Unsuccessful AR operations triggered us to study and model entire phenomena in Power System Analysis software (EMTP).


Initially, two circuits of 765 kV Transmission Line commissioned between Generation Station and Transmission Station with Line Reactor and NGR in both line at either end. Successful auto reclosure observed during single-phase faults on these lines. Intermediate Switching station constructed and both lines were divided in 4 section as per new requirement. Same configuration (rating) of Line Reactor and NGR adopted at newly constructed station on each line. Unsuccessful AR observed during AR running cycle on these lines after new configuration. Backup Impedance protection of Line Reactor found operated during AR Dead time.
Different sets of simulations has been carried out to understand the phenomena:

- Single Phase fault and Auto reclosure in 765 kV Transmission line in different section of entire corridor with Varying Shunt compensation (Value of Line Reactor)
- Different NGR values and observations for above simulations
- Trip the Line Reactor Breaker during Auto Reclosure Phenomena to avoid operation of Backup Impedance protection and its consequences

After EMTP Simulations and study, it was concluded that:

- Line Reactor (Degree of compensation) should be adjusted with adequate value while line length altered from its original design.
- NGR re-sizing can address the issues at some extent. Suitable value of NGR (based on Line Length and amount of shunt compensation) should be employed
Appropriate Solution and mitigation suggested after detail simulation & study.

Tag(s): single pole, analysis, auto reclosure, line reactor

Modeling and evaluation of overvoltage792

Abstract
A case study will be presented demonstrating modeling of overvoltage in a moderately sized system involving medium voltage vacuum breakers, cables and transformers. The focus is on simulating high fre... see morequency overvoltage generated by circuit breaker prestrikes and re-ignitions and evaluating the impacts on transformer insulation.
-Results obtained from a customized breaker TRV model which is capable of controlling the capability of switching high frequency current will be presented.
-The methodology of analyzing severity of overvoltage in the frequency domain was applied in this project. Results and discussions regarding frequency domain analysis will be shared.
-Simulation results regarding typical system configurations with variation of key parameters such as cable lengths, load power factors will be briefly presented.
-Application of EMTP study results in assisting equipment specification, as well as overvoltage mitigation methods including optimizing switching sequences, necessity of snubber circuits will be discussed.
-Case specific strategies to improve simulation speed and work flow with EMTP will be introduced and discussed.