When capacitors are disconnected from the supply, a DC voltage persists across the terminals of the capacitor unit. Safe handling of capacitor units after de-energisation requires that the stored electric charge in the capacitor unit should be removed to avoid the risk of electric shock to personnel. Any stored charge should be removed gradually — shorting the terminals of a capacitor unit to remove the charge will result in very rapid discharge of a substantial amount of energy that can endanger personnel and result in damage to the capacitor units themselves.
Capacitor units are therefore supplied with a discharge device capable of reducing the voltage between the terminals practically to zero, within a given time, after the capacitor has been disconnected from a network. The question of what this discharge time should be is of interest in this article.
The decision of a shorter discharge time for a capacitor bank may seem safe and harmless. In fact such a decision results in possible long term damage to the the capacitor units, and will always have a significantly higher carbon footprint than the default IEC60871 discharge time.
Shunt capacitor banks are expected to operate for many years in harsh electrical and environmental conditions. Conservative designs are therefore preferred from a technical perspective. On the other hand, commercial preference is for least cost designs.
This note reviews the requirements for capacitor voltage rating and reactor current rating in two common situations. The purpose is to determine component ratings according to the requirements of standards such as IEC 60871 that will result in reliable performance under foreseeable operating conditions.
We are experts in reactive power compensation design, manufacture, delivery and operation. Feel free to contact us for more information or assistance.
Induction and synchronous motors draw starting current that is considerably more than nominal current. This can cause voltage sags that exceed permissible levels as determined by supply agreements, cause problems for equipment in the remainder of the plant, and in worst cases cause the motor to stall. Optimised Network Equipment can provide a solution based on rugged thyristor switched capacitor banks that has lower cost compared to other remedies such as variable speed drives, provides near full torque during starting and is very simple to install indoors or outdoors in a switchyard.
This example delivered by GE Grid Solutions to the Colonial Pipeline Company describes the typical problem, alternative remedies and a comparison of advantages and disadvantages for each. Refer to our downloads section for product information.
We can provide support in terms of dynamic system models that will identify potential starting voltage sages, quantify the problem and the details of the required solution. Please contact us for more information.
All our clients have access to the combination of excellent quality products backed by specialist local and international engineering skills to develop and deliver solutions at all levels of the energy business.
For example in this article design aspects of mechanically switched capacitors with damping networks (MSCDN), also called “C-type filters” are presented, with relevant information and recommendations regarding the specification and protection of the filter components. Innovative relaying schemes are presented to ensure reliability and sensitivity for internal faults on the components, in particular air-core reactors, in order to avoid major damage to them and allowing further analysis of the causes of faults.
The combination of our ability to model and understand your electricity network and the support of excellent engineering and production resources internationally provides our clients with un-equalled confidence in the solutions they implement. Contact us and experience it for yourself.
It is a great pleasure to announce that due to the acquisition of Alstom Grid by GE, and the subsequent formation of GE Grid Solutions, we can now serve our customers even better with an expanded, fully resourced and competitive product range of reactive power compensation solutions. The formal transaction occurred on Monday 2 November 2015.
Our full product range is available on the download page. Here are some extracts:
As always we look forward to serving our customers by adding value to their businesses with our local expertise, excellent quality products and project delivery capabilities.
We provide solutions based on strong technical merits and a professional approach to our business. An example of our approach can be found in our solution for enclosed capacitor banks as described in this article. We understand that buyers, users and suppliers all have somewhat different histories and preferences, and we aim to provide a clear description of the most important things to look out for in the specification, procurement, design, manufacturing, delivery and operation of enclosed medium voltage capacitor banks. We would be delighted to discuss this in more detail with you.
We support our power industry customers from concept designs, power system analysis, product selection and all the way through their project delivery. Our specialists are available to provide you with all the detailed product and application information you need for optimised, best quality solutions.
These are not empty words. Our recent recertification to ISO 9001:2008 demonstrates that all our activities are governed by our quality system. Our customers see the benefits of dealing with a lean, technically expert supplier that does not compromise on quality when advising on, designing, or delivering reactive power compensation solutions.
Contact us at any time and we will work hard to optimise your network.
What do you get when you combine the best performing active harmonic filter on the market with on-site evaluation and detailed application engineering support? The MaxSine Compact: it ticks all the boxes:
- Modular design from 50 A to multiples of 100 A
- Flexible mounting in OEM panels, wall or floor mounted cubicles
- Several control options for fast and super fast (<1 ms) compensation
- Neutral current compensation
- Reactive power compensation
- Powerful yet simple setup by means of web browser interface
Applications range from anywhere with electronic loads that are sensitive to power disturbances like hospitals and office blocks, to any fast changing linear or non-linear load.
Optimised Network Equipment has the necessary measurement equipment to evaluate your requirements on site, and can carry out efficient studies to confirm your exact requirements for harmonic filtering – active or passive – no matter what your location or application.
Harmonic filters remove harmonic current from the network and improve load power factor. Some applications require harmonic mitigation without any significant reactive power contribution, for example when non-linear loads operate at close to unity power factor and the network cannot accept leading reactive power.
ONE has designed, delivered and tested solutions based on harmonic filters that draw current only at harmonic frequencies, and describe the design and steady state and transient performance in a technical note. The outcome is a passive filter circuit that is an effective solution of harmonic distortion yet that draws almost no fundamental frequency current, and has no onerous switching requirements.
Please contact us if more information is required.