Technical Presentations

Study of Sub-synchronous Resonance for thermal power plants connected on Vietnamese grid using EMTP®867

Abstract
Study of Sub-synchronous Resonance for Thermal Power Plants Connected on Vietnamese Grid Using EMTP

Tag(s): Synchronous Machine, Subsynchronous Ressonance, Undamped Oscillations, FACTs, Series Compensation, TCSC, STATCOM

Ferroresonance Phenomena for Voltage Transformer failure – Simulation & Analysis using EMTP and Mitigation Technique874

Abstract
Ferroresonance is an oscillating phenomenon between a non-linear inductance and a capacitor that can results in highly distorted over voltages and overcurrent. Ferroresonance phenomenon occurs when a ... see moreferromagnetic core inside an electrical device – primarily a voltage transformer or an unloaded power transformer – operates in the saturated condition, under which inductance has become a non-linear element. In practice, ferro resonance can be triggered even by a temporary introduction of core into saturation, e.g. resulting from switching operations or a change in voltage resulting from an earth fault.

Tag(s): Ferroresonance, Transformers, Low-Frequency Transients, Overvoltage, Non-Linear Element

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

Real Case of a Resonance in a Power Plant851

Abstract
Overvoltages were identified on the MV and LV networks of a Hydro Power Plant as the cause of the trip of the LV maximum voltage protection, compromising the normal operation of the system. Following ... see morethis event, measurements were conducted and the presence of a very high 23rd harmonic, potentially responsible for the various overvoltages, was identified associated to the operation of the Plant’s Synchronous Machine Frequency Control System (FCS). It was concluded then that this harmonic would have its origin in the FCS and would be amplified due to a possible resonance in the Power Plant internal network. A digital simulation study, using EMTP, was conducted to identify and characterize the resonance in the system and to propose mitigation solutions. The simulation models were developed using the equipment data and the system characteristics. The models were duly validated with measurements made both in time and frequency domains and it was possible to identify the origin of the overvoltages and their propagation in the system. It was concluded that the resonance occurred between a 30/11 kV Power Transformer and a 30 kV cable with 850 m.

This conclusion was supported by the results obtained in the measurements. Several alternatives were analyzed as mitigation solutions: - Installation of capacitors; - Different bonding techniques of the 30 kV cable sheaths; - Changing the 30 kV cable length; - Installation of a harmonic filter; The advantages and disadvantages of each solution were weighed also considering the ease of implementation, namely the available room. It was concluded that the installation of capacitors would be the best option. Measurements were conducted after the capacitor’s installation confirming the success of this solution.

Tag(s): harmonics, power uality, resonance

Wind & Solar Generation Impact on Negative Sequence & Power Swing Protection759

Abstract
<p>This presentation investigates the impact of wind generation on the performance of negative-sequence-based protection.</p><p>
Overview: - Main differe... see morence between EMT-type and phasor domain software. - Load-flow simulations - Time-domain simulations - Frequency Scan - Statistical runs for Insulation Coordination studies - Switching - Lightning - Transient Recovery Voltage (TRV) - Ferroresonance - FACTS/HVDC - Transient stability - Renewable - Power quality - LVTR/OVRT - Sub-synchronous resonance (SSR) - Overcurrent protection - Differential protection - Distance protection - Power-swing and out-of-step detection - Loss of field protection - Open-phase</p>