Technical Presentations

Capacitor energization, power system conversion, and load flow studies in EMTP858

Abstract
The addition of capacitor banks to the system may result in the frequency shift of the resonance modes in the system. This change may result in undesired interaction of the system with other elements ... see moreduring the transients. In addition, the energization of the capacitor banks may result in undesired over voltage and high inrush current (above the breaker capability limits).

Following steps has been taken to ensure the addition of the new cap bank to the system will not adversely affect the performance of the system

• System conversion to EMTP from PSSE using import tool function in EMTP for 5 busses away from the system
• Running the load flow and benchmarking the results
• Running the frequency scan of the system
• Performing the transient studies for 100 breaker closing instances
• Perform the statistical analysis (available tool in EMTP)
• Perform the worst-case scenario achieved during the statistical analysis

Tag(s): capacitor switching, overvoltage, inrush current, PSS/E import tool, frequency scan, statistical analysis

Current Zero-Missing Phenomenon for Shunt Compensated Transmission Lines860

Abstract
The presentation shows the ZMP at the line and shunt reactor breakers using EMTP simulations performed while planning a large wind project in the USA. It also include a discussion on the mitigation me... see moreasures.

Tag(s): shunt reactor, transmission lines, current-zero missing, line energization, unbalanced fault

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

Insulation Coordination Study of 765kV GIS SUBSTATION788

Abstract
Gas Insulated Substations provide cost effective solution due to reduced land requirements particularly in metropolitan area where power demand is registering steep growth. With the use of GIS technol... see moreogy, it is required to assess the risk of failure due to overvoltage. The Insulation Coordination study forms a very important aspect in design stage. This presentation deals with the IC study carried out for a large – 765/400/220kV GIS substation in a SUPER THERMAL POWER STATION in UTTAR PRADESH.


Due to the decreasing ratio of lightning impulse withstand voltage to the system voltage, the difference between LIOV and VFTO decreases and this factor calls for VFTO performance analysis for 765kV GIS as well.
The discussion includes modeling of Extra High Voltage GIS, Temporary Overvoltage (TOV), Lightning Impulse Overvoltage (LIOV), Switching Overvoltage (SOV) and Very fast transient Overvoltage (VFTO) performance analysis on 765kV GIS substation.
TOV typically caused by fault to ground, load rejections and energization of long lines are analyzed to decide the rating of the surge arrester.
LIOV simulation studies are carried out for possible onerous paths including longer and short paths to decide the location of the arrester. SOV analysis deals with the overvoltage due to switching operations during line energization, re-energization and fault occurrence and clearance.


The LIOV and SOV results have been validated with reference to protective levels prescribed. The VFTO analysis is performed with various GIS disconnector operations in accordance with the methodology and guidelines as per CIGRE WG D1.03-TB 519 and the results are validated with the limits specified.
Keywords: Insulation Coordination, VFTO, EHV, GIS, 765kV, Protective ratio.

Synchronous condenser transformer energization with PAMSUITE781

Abstract
In engineering studies, getting the necessary input data for performing EMTP simulations may be one of the most challenging tasks.
Indeed, the characteristics of the system under study are usual... see morely badly known for a number of reasons: sometimes they are known with some inaccuracy.
For example when parameters are associated with tolerances; sometimes, the characteristics are completely unknown, for example when the equipment is very old and the datasheets are not available, or when the study is about a future project for which many equipment characteristics are not known yet.