closed transition manual transfer switch

The switch will operate in a make-before-break mode provided both sources are acceptable and synchronized. Typical parameters determining synchronization are: voltage difference less than 5%, frequency difference less than 0.2 Hz, and maximum phase angle between the sources of 5 degrees. This means the engine driving the generator supplying one of the sources generally must be controlled by an isochronous governor.If either source is not present or not acceptable (such as when normal power fails) the switch must operate in a break-before-make mode (standard open transition operation) to ensure no backfeeding occurs.This requires getting approval from the local utility company.A CTTS is not a substitute for a UPS (uninterruptible power supply); a UPS has a built-in stored energy that provides power for a prescribed period of time in the event of a power failure.Because there are no mechanical moving parts, the transfer can be completed rapidly, perhaps within a quarter-cycle of the power frequency.Different models are available, with both manual and automatic transfer. Often small transfer switch systems use circuit breakers with an external operating linkage as the switching mechanism. The linkage operates two circuit breakers in tandem, closing one while opening the other. Manufacturers of transfer switches can provide installation guides to select the size of switch and provide recommended installation procedures. By using this site, you agree to the Terms of Use and Privacy Policy. While open transition and delayed transition switches offer reliable performance, they also interrupt power flow to loads during each transfer. Alternatively, Closed Transition Transfer Switches (CTTS) transfer loads without interrupting power when both power sources are available and each presents acceptable characteristics. While open transition and delayed transition switches offer reliable performance, they also interrupt power flow to loads during each transfer.

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Some transfer switches are manual, in that an operator effects the transfer by throwing a switch, while others are automatic and trigger when they sense one of the sources has lost or gained power.The transfer switch isolates the backup generator from the electric utility when the generator is on and providing temporary power. The control capability of a transfer switch may be manual only, or a combination of automatic and manual. The switch transition mode (see below) of a transfer switch may be Open Transition (OT) (the usual type), or Closed Transition (CT)). Once the ATS sees that the generator is ready to provide electric power, the ATS breaks the home's connection to the electric utility and connects the generator to the home's main electrical panel. The generator supplies power to the home's electric load, but is not connected to the electric utility lines. It is necessary to isolate the generator from the distribution system to protect the generator from overload in powering loads in the house and for safety, as utility workers expect the lines to be dead. Some transfer switches allow for load shedding or prioritization of optional circuits, such as heating and cooling equipment. More complex emergency switchgear used in large backup generator installations permits soft loading, allowing load to be smoothly transferred from the utility to the synchronized generators, and back; such installations are useful for reducing peak load demand from a utility.A break-before-make transfer switch breaks contact with one source of power before it makes contact with another. One example is an open transition automatic transfer switch (ATS). During the split second of the power transfer the flow of electricity is interrupted.There are also operational conditions where it may be desirable to transfer loads with zero interruption of power when conditions permit. For these applications, closed transition transfer switches can be provided.

It is this current surge that can trip breakers or, in more extreme cases, damage equipment. Breakers, transfer switches, and cable must be sized accordingly. IEEE 1547 allows generator sets or systems of paralleled generator sets between 1.5 and 10 MVA to be up to 10 deg out of phase with the utility when closing to the grid, with higher phase difference limits for smaller systems. For other equipment the answer depends on how much surge current the system can handle without tripping breakers or damaging equipment. For high reliability, one must consider the magnitude of current that can flow between the sources at the instant of transfer. Surge current can be modeled as: In many applications where a single standby generator set is backing up the utility, the impedance at the instant of closure will be dominated by the subtransient reactance of the alternator. However, a thorough analysis will include all the sources of impedance in the calculation. Note that in applications with paralleled generators, one must account for the contribution to the current from all the generator sets. This can be done by calculating an equivalent subtransient reactance for the paralleled generators according to the following equation: With this assumption, surge current can be modeled as: Figure 1 is a representation of two voltage sine waves that are 10 deg out-of-phase and the difference between the two waveforms at each point in the cycle. The dashed line represents the instantaneous voltage difference between the two sources. This line is also a sine wave at the same frequency as the two sources. The maximum voltage on this line is the worst-case scenario for the differential voltage at the instant the two sources are paralleled. The worst-case voltage in this case is 0.17 per unit (pu). In the data sheet in Figure 2, we see that the alternator has a subtransient reactance of 0.144 pu based on an alternator kVA rating of 3660 kVA.

Alternatively, Closed Transition Transfer Switches (CTTS) transfer loads without interrupting power when both power sources are available and each presents acceptable characteristics. This term reflects the sequence of switching mechanism operations, where the contacts for the original source are opened before the contacts for the alternate source are closed.The sequence is similar to open transition switching; however, the duration of the power interruption is extended to allow residual voltages to decay and motors to slow. This avoids the occurrence of large inrush currents when the switch closes on the alternate source.This results in momentary source paralleling that provides continuous power, avoiding momentary power interruption to sensitive loads. Closed transition switching requires care to avoid extended interconnection of the sources, and should never be used without consulting utility officials.In this mode, however, the sources can be paralleled for extended periods. This highly advanced sequenced is used to decrease loading on the original source while increasing loading on the alternate source. Used only in highly specialized applications, soft-load Automatic Transfer Switch (ATS)’ can be used to avoid both power interruptions and rapid changes in power conditions. Unlike the other modes that are illustrated using voltage, soft-load is best understood by observing temporal changes in power. Click Here The benefits are that the emergency power system can be tested without interrupting power to loads and power can be retransferred to the utility after a failure without interrupting power to loads. However, there are risks associated with closed transition transfer switches as two live sources are connected together. The difference in voltage can be caused by several factors: This current is limited only by the impedance of the sources and the current-carrying capacity of the cable or bus connecting them.

1 Hz has been used effectively. Many synchronizing systems also include a voltage matching function, in which the generator sets will adjust the voltage regulator to drive the generator voltage level to match the utility voltage level. The voltage matching function is important in applications where the voltage on the utility transformer varies with load. Note that the utility waveform is constant and the synchronizer drives the generator set waveform in to sync with the utility. The voltage matching function forces the generator voltage to be at the same level as the utility voltage. Load changes on a system bus cause a sudden change in phase angle difference as frequency surges or sags in response to the load transient. This can cause the two sources to momentarily be out of sync until the synchronizer forces them back into synchronization. This is why for systems with multiple closed transition transfer switches, best practice is to allow only one switch to transfer at a time. With an active-phase lock-loop synchronizer, the time to synchronize is relatively short and reliable, so timing between switch operations need not be long. For this reason the possibility of load transients at the moment of transfer should be minimized. For systems with multiple transfer switches, best practice is to allow only one switch to transfer at a time. This can best be achieved either by staggering transfer time delays or by using the transfer and retransfer inhibit functions. When transferring loads with closed transition transfer switches, only one transfer switch should be allowed to transfer at any given time. All switches initially are inhibited from transferring and the master releases the inhibit on one switch at a time. For example, consider the system in Figure 4 consisting of two closed transition transfer switches. The normally closed aux contact from the normal side of the automatic transfer switch (ATS) 1 is wired into the retransfer inhibit input ATS 2.

When adding per-unit quantities, the per-unit values for the alternators and transformer must be based on the same base kVA rating. Circuit breakers typically have their instantaneous trip current set to 7 to 10 times the long time-trip setting. The surge will last only for one or two cycles, so as long as the level of surge current is not in the instantaneous trip range of the breaker, the breaker will not trip. Keep in mind that if the breaker is a current-limiting breaker designed to trip in the first half cycle of a fault, this will have to be considered. This will not cause a problem for the switch or the breakers. However, if this load were being transferred by a 400-amp transfer switch protected by 400-amp breakers located lower in the system, there is now a chance that the current surge will trip one of the breakers. Equipment must be sized to handle the surge current. Where this is not practical, open transition switches should be used. Loads that cannot tolerate a momentary interruption in service should be fed by an uninterruptible power supply (UPS). Transfer switches use a sync check function for initiating closure to the oncoming source when the two sources are in phase. There are two basic algorithms used by sync check systems: a permissive window algorithm and a predictive algorithm. When the three parameters are within some predefined limits, the sources are said to be within a “permissive window.” When the sources have been in the permissive window for some preset period of time, the controller closes to the oncoming source. The required time in the permissive window is typically set to 0.1 to 0.2 seconds for passive synchronizing systems and 0.5 seconds for active synchronizing systems. Generally speaking, the permissive window algorithm is more robust because the predictive algorithm is susceptible to transients on the voltage sources, which could skew the calculation of the optimum phase angle. A slip frequency of 0.

It can be an issue in applications where a residual voltage is briefly maintained at the load due to the generator effect created by a rotating motor or by the stored energy released from a transformer’s windings or core. Operation is independent of electrical synchronization between both sources of power. A transfer between power sources can be initiated automatically or manually. Disadvantages Unless some type of stored energy system, such as an uninterruptible power supply (UPS), is located downstream of the transfer switch, loads will experience a brief interruption in power during the transition delay period. In-phase transitions are typically completed in 150 milliseconds or less to ensure that inrush current is equal to or less than the normal starting current of the inductive load(s). If synchronization doesn’t occur within that time span, some transfer switches have the ability to default automatically to a delayed transition that serves as a failsafe. Advantages The rapid transfer time means that a transfer is accomplished without an appreciable power interruption to the load, provided that the system is properly adjusted Disadvantages In-phase transitions must be executed by an automatic controller. Manual operation is not possible as microprocessor logic is needed to manage source synchronization. If both sources of power are available but unable to meet pre-set synchronization criteria, and the transfer switch isn’t capable of defaulting to a delayed transition, a transfer will not occur. As there’s no gap between disconnection and connection, downstream loads receive continuous power throughout the transfer process. Switches configured for closed transitions usually transfer power automatically as soon as both power sources are closely synchronized in phase, voltage, and frequency.

The overlap period during which both sources are simultaneously connected, or “paralleled”, usually lasts no more than 100 milliseconds to comply with local utility interconnect requirements. Advantages Critical loads can continue to operate, without an interruption in power, during loaded generator engine testing Energy costs can be reduced through “peak shaving”, which is the ability to control usage from a utility during intervals of high demand in order to limit or reduce demand penalties during a given billing period Depending on the application, may eliminate the need for a UPS to be located downstream Disadvantages Transfer switches sophisticated enough to execute a closed transition tend to cost more. Some utilities require closed transitions to comply with interconnect requirements aimed at preserving power quality and protecting utility service personnel and equipment. In some cases, this can require the inclusion of protective relays in the electrical circuit Closed transitions must be executed by an automatic controller. Manual operation is not possible as microprocessor logic is needed to manage source synchronization Closed transitions can produce higher fault current, due to the 100 millisecond period when both power sources are paralleled. As a result, the consulting engineer may specify a higher withstand close-on rating (WCR), which could require oversizing the transfer switch amperage rating. It helps you to shape up your technical skills in your everyday life as an electrical engineer. More Information Edvard Csanyi Electrical engineer, programmer and founder of EEP. Any diagram illustration will be much appreciated or video. Thanks! Reply Vladimir Monev Feb 17, 2017 Is there any transfer swich for open transition switching like (I-0-II),but when you are in the 0-transition there is a connection between the load and “0” and it can serve as a grounding switch.

This will inhibit ATS 2 from beginning its retransfer sequence (including all time delays) until after ATS 1 has transferred back to the normal source. If the first switch fails to transfer or if the aux contact fails, the second switch will not transfer without manual intervention. For this reason it is preferable in some cases to use staggered time delays to prevent the switches from transferring at the same time. As these time delays are typically set on-site, it is important to clearly specify the time delays in commissioning documentation. It is not a requirement in the event of a utility failure, so there is no need to be concerned about not getting the emergency source online quickly enough. Many transfer switches have a “fail to disconnect” output which can be used for this. It is up to the installer to connect these devices to the shunt trip of the breaker. Some utilities require maximum parallel timer and lockout relays that are separate from the transfer switch control to implement this function. Tripping either the normal side or emergency side breaker will provide the same level of equipment protection, although many utilities require tripping the normal side breaker. This is a significant benefit in some applications; however, there are risks associated with closed transition transfer as two live sources are connected together. For loads that are not protected by a UPS, it is worth considering if the value of not having an interruption during a test or a retransfer to the utility justifies the risk of a closed transition transfer. Scroggins has been with Cummins for 18 years in a variety of engineering and product management roles. He has led product development and application work with transfer switches, switchgear controls, and networking and remote monitoring products, and has developed and conducted seminars and sales and service training internationally on several products.

Rich received his BSEE from the University of Minnesota and an MBA from the University of St. Thomas. A typical transfer sequence includes following steps: The normal power source fails. When power from the generator or the backup utility feed is stable and within prescribed voltage and frequency tolerances, the transfer switch shifts the electrical load to the emergency power source. Depending on the facility’s needs and preferences, that transfer either occurs automatically or is executed manually. When utility power is restored, the transfer switch returns the load from the emergency power source to the normal one. Again, this can happen automatically or manually, depending on the type of switch being used and its operation mode. ATS panel (photo credit: methodstatementhq.com) Two ways to transition loads Transfer switches can transition loads between normal and emergency power sources in two basic ways: Open or Closed The specific functions performed by a given load and the importance of those functions to safety or security play an important role in determining which kind of transition is required. That is, the transfer switch breaks its connection to one power source before making a connection to the other. For some period of time between disconnection and connection, neither the normal power source nor the emergency source is providing electricity to downstream loads. That delay typically lasts either a specific, pre-set amount of time or however long it takes the load voltage to drop below a prespecified level. Advantages Building a delay into the transition process can prevent higher than normal electrical current ( also known as “inrush current” ) from developing. Inrush current can occur when an inductive load is rapidly reconnected to a non-synchronized power source.

Reply mohsen Dec 19, 2015 hello please give me information about changeover switch (make before break motorize) in below circuit Q01 WHAT KINDE OF SWITCH IN YOUR PRODUCT. THANKS Reply Leon Venter Jun 04, 2015 Edvard, Well done on a clear article. With the increasing incidence of Load-Shedding occurring in many of the counties I work in, the question of Automatic-Change-Over from Supply Authority to Stand-By Generator is becoming normal practice. Regarding the question of “what is critical and non-critical” loads it depends on the consumers operation. Is it a Hospital with life-support then it would be important to have this equipment to be un-interrupted i.e. UPS, if not then the process must be changed over ASAP. If the consumer has critical materials in a process, say a glass-works or a plastics-works then the supply must be returned within a suitable time to prevent the product from solidifying in the moulds. Most of my experience with stand-by generators allows for a change-over ATS using contactors with a suitable mechanical and electrical interlocking. When there is load-shedding the generator is allowed to get up to voltage and the contactor for the generator comes in. (so the time lost is Generator start up time plus a few seconds. Once the supply comes back on the generator continues to feed the plant for a pre-determined time to ensure that the supply authority supply is stable then the question is how do you switch back to the supply authority. Most of the time there is a further Off sequence where the supply is disconnected from the generator, there is a time lag where any rotating equipment is allowed to wind down then the interlocked contactor system switches back to the main supply and the machine operators bring back the machinery to full operation.

With the advent of micro-processor change-over and the ability to monitor the supply and generator phase sequences there is a new generation of switches where the hand over is instantaneous and there is no loss of supply at this switch over sequence. Perfect synchronised hand over, no loss of supply and very little inrush current. Reply Leave a Comment Cancel Reply Tell us what you're thinking.Plans and Pricing Log In Facebook Linkedin Linkedin Twitter. Some of these cookies are set automatically because they’re necessary for the site to perform. Other cookies are used for functional, performance, and targeting purposes to enhance your experience by personalizing content and ads, enabling third party content and features, and enabling us to analyze how this site is used. To learn more, please visit our Legal Notices - Cookie page. By clicking 'I Accept', you are agreeing to our use of functional, performance and targeting cookies. Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.Or, onboard construction technology that helps you get to grade faster, hit target payloads, and keep you safe.

Our dealer locator provides the most up-to-date information on Cat dealers close to you. Simply enter your address and select the type of equipment you're looking for. Or, if you already know the name of the dealer you're searching for, you can type in the dealer's name for a list of locations. They provide flexibility, reliability and value in a compact package. A Bypass Isolation Automatic Transfer Switch (ATS) provides fully functioning transfer in applications where emergency power to critical loads must be maintained at all times with no interruption. This type of design allows for inspection, maintenance or replacement of the power switching mechanisms with no interruption in electrical service. Breaker based Bypass isolation ATS are available from 200A to 5,000A. The hinges have removable hinge pins to facilitate door removal for easy wall mounting or service and are supplied with pad-lockable latches. Cat experts work with you to design a system to meet your individual power needs. Your Cat dealer can help you maintain that built-in value through a Customer Value Agreement (CVA). Find what you’re looking for.Sign up below for additional information. Or for instant access, you can skip this form. Click here Some of these cookies are set automatically because they’re necessary for the site to perform. Other cookies are used for functional, performance, and targeting purposes to enhance your experience by personalizing content and ads, enabling third party content and features, and enabling us to analyze how this site is used. To learn more, please visit our Legal Notices - Cookie page. By clicking 'I Accept', you are agreeing to our use of functional, performance and targeting cookies. By staying here you are agreeing to our use of cookies.

Our breakthroughs in transfer switch technology enable us to offer one of the most comprehensive and advanced portfolios of transfer switch solutions in the world, from well-established technologies to the latest in digital innovation. With ABB, you can choose the functionality and features that are just right for your facility, knowing that you’ll get outstanding reliability, even in the most demanding conditions.By significantly reducing the number of connection points, ABB increases reliability and decreases the likelihood of downtime of your most critical loads and processes. In addition, we offer solutions with fast in-phase transition and closed transition to reduce outage time. Operators can measure and monitor a wide variety of parameters to stay proactive, save time, and reduce costs. Available safety features include mechanical isolation of unsynchronized power sources, manual emergency operation, and protection from current-carrying parts to reduce the risks for operator injury. Unmatched performance. Transfer switches allow the Emergency Power Supply (EPS) (i.e. genset) to assume the electrical load from the primary power source (i.e. utility) during a power outage. There are two types of transfer switches. ATS’s use undervoltage-sensing devices to monitor the primary source of power. The ATS: It is not necessary to use switches listed for emergency service to transfer loads not designated as emergency. ATS’s transfer load from one power source to another by opening and closing contacts that are connected to the primary power supply and the backup power source. Different configurations are available depending on the application including: Certain applications may use closed-transition or soft-load transition switching, which allows momentary paralleling of the generators with the utility. Closed transition switching is used in applications where the interruption of power even for a few milliseconds is not acceptable (e.g. hospital operating rooms).

However, this equipment should be approved by the local utility and the authority having jurisdiction (AHJ). The system shall also be designed so that, upon failure of one or more engine generator sets, the load is automatically reduced (shed), starting with the load of least priority so that the last load affected is the highest priority or emergency load. Setting time delays while staying within the required time required for power restoration by the Type of EPSS can also help generators to stabilize voltage and frequency. The primary purpose of a bypass-isolation switch is to allow safe access for inspecting, maintaining, or servicing the switch without interrupting power to critical loads. A short-circuit and selective coordination study would need to be performed by a qualified engineer to determine the maximum available short-circuit current at the service and all switchboards, panels, and transfer switches. Switching Control logic continuously Closed-Transition Transfer within 5 electrical degrees is Therefore, Plus, protective relaying may not be required under Failure to synchronize indication and extended parallel time Applications include older style variable frequency drives, rectifier banks, and load management applications. The bypass switch has dead front quick-make, quick-break operation for transferring of loads between live sources. That’s hopefully straightforward ( click here to read some background on ATS ), but from here we now have several options we unpack with our clients, based on the type of transfer switch and how their application can effect or better suit their site. We will relate these to a typical mains generator application, but they can be applied to switching between other power sources also.