Metal Enclosed Voltage Regulators (2.4 - 34.5kV)

With the addition of new United States Embassy sites going in all over the world, Gilbert Electrical Systems along with our local sales representative has worked closely with the US State Department in developing a specification for metal enclosed voltage regulators. Enclosing voltage regulators in a metal housing along with the proper bypass switches and fused disconnects not only provide security in a hostile environment but also gives the user a turn key project for system regulation. Voltage regulators can be thought of as a step auto-transformer. Normally, by control sensing, these regulators step the voltage up or down in increments when the system voltage becomes to high/low. By doing so you provide a clean steady source of power to the transformer feeding the loads. This not only protects your load but it also helps to protect the transformer from stray voltages and transient currents.

Bypass switches and fused disconnects are also provided. The fused disconnect provides fuse protection and isolation for the transformer and the regulators. Coordinating the fuse with the transformer can be accomplished by Gilbert Electrical Systems given the ratings of the system and ratings of the transformer. Adaptive throat connections can even be provided for direct mounting the transformer to the regulator enclosure.

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Figure 1
Each regulator is provided with its own bypass switch. The function of bypass switches allow the user to remove a regulator from service without interrupting the system. On a single pull bypass switch the regulator is de-energized and the phase voltage is redirected. This is useful when the system can’t be interrupted due to regulator failure or when a regulator is scheduled for routine service. Each bypass switch is provided with an arc interrupter to help eliminate arcs during operation.

NEMA 2 hole terminating pads are provided at both the incoming and transformer connections of the regulator enclosure for ease of installation. Arresters can also be provided at the incoming to help provide over-voltage protection for the electrical system. Each regulator is conveniently located in a separate bay for easy removal or maintenance. See figure 1.


Regulators can regulate a single or a three phase circuit using any combination of one, two, or three regulators. Two regulators can be connected open-delta to regulate a three phase, three wire WYE system. To help explain the different connections, below is a series of diagrams to help illustrate the typical connections of regulators.

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Figure 2: Single-phase, Two Wire Circuit.
Single phase, two wire circuits require one regulator only with a single bypass switch for complete operation. A fuse and disconnect switch may be added but is not typical for single phase systems. Single phase connections are typical when using single phase conventional transformers. These are commonly seen on distribution lines where space is minimal. See figure 2.
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Figure 3: Three-phase, Three Wire WYE or Delta Circuit.
Regulating a three phase, three-wire system is no problem by using two regulators connected in an open delta. Single pole disconnects must also be used to totally isolate the regulator for maintenance. A three pole group operated switch and primary fuses are normally provided for the protection and isolation of the transformer. Eliminating the third regulator and bypass switch not only saves money but also space in a limited environment. See figure 3.

Regulating a three phase, three-wire system is no problem by using two regulators connected
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Figure 4: Three-phase, Three Wire Delta.
Three phase, three wire circuits require three regulators and three bypass switches. This approach uses single pole disconnect switches to isolate a regulator from the system for removal or maintenance. A three phase group operated switch and primary fuses are also added for transformer protection/isolation as shown in figure 4. This arraignment can be connected for systems up through 35 KV. The US State Department has standardized on this connection for all newly constructed embassies.
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Figure 5: Three-phase, Four Wire WYE.
Three phase, four wire circuits require three regulators and three bypass switches. There is no need for single pole disconnects on the SL bushing of the regulator for this bushing is grounded. Typically this is the easiest of the different connections to maintain and service this connection is also the most cost efficient of the three phase systems. Using a common neutral/ground eliminates the need for series connections of the SL bushing as shown in figure 5.

Each circuit represented above shows a single pole bypass switch, pole mounted single phase regulators, single pole disconnects Each circuit represented above shows a single pole bypass switch, pole mounted single phase regulators, single pole disconnects for regulator isolation and primary switching and fusing. A variety of combinations are possible and only the typical ones are shown above.

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Figure 6
System metering can also be provided in a regulator enclosure by the addition of another bay. As seen in figure 6 to the right, three potential transformers and three current transformers have been added to monitor the users system. These PT’s and CT’s are situated for easy access and maintenance. The PT’s and CT’s are then wired to a terminal block positioned in a convenient location for the user to connect to. Meter sockets and meters may also be provided if given the specific type and model of both.

The pro’s of using regulators enclosures are vast. Not only do you protect the regulator from hostile acts of vandalism, terror and war time acts but also from the weather and wildlife which will prolong the life of the regulator. Gilbert Electrical enclosures have been approved for a seismic 4 event due to the rugged environment which it may be situated.

By using single phase regulators in lieu of a three phase pad-mounted type regulator, you eliminate the worry of losing a phase and having to replace the entire regulator. Also, by purchasing the complete lineup you have a turn key unit. If purchasing all item separate, you must find real estate to mount the regulators, bypass switches, single pole disconnects, primary fusing and group operated disconnect. Not only do you have to position each item for ease of access and maintenance you must wire/connect these items together. In a three phase, delta configuration this can be quite troublesome and time consuming. All of this is eliminated with a regulator enclosure. Some of the projects completed by Gilbert electrical include US Embassy Nairobi, US Embassy Dar Es Salaam, US Embassy Zagreb, US Embassy Angola and US Embassy Abuja, in Nigeria. Gilbert has projects here in the US as well which include many hospitals for power regulation.

Typical Regulator Enclosure Lineup
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Bay #1
Bay #2
Bay #3
Bay #4
Bay #5
Figure 7

Figure 7 shows a typical regulator enclosure lineup consisting of a five bay enclosure. A primary disconnect switch is located in the left most bay #1. Next, the bypass and regulator isolation switches are located in bay 2. Bays 3, 4 and 5 house the three regulators in a three phase system. All panels are removable and are secured with tamper resistant hardware. Customer connections for the incoming power feed and outgoing transformer feed are located in bay 1 and the rear of bay 2 respectively.

Additional Photos of Voltage Regulator Assembly
Gilbert Electrical Systems
Gilbert Electrical Systems
Figure 8


The enclosure is fabricated of not less than 11 gauge mild steel with the necessary angle and/or channel base frame for regulator support. Units may also be constructed from 304 stainless steel, 316 stainless steel or aluminum. Each section shall be provided with a minimum of 4 lifting lugs for shipping and lifting the unit. All roofs are crowned with rain troughs between sections for proper water drainage. All corners are formed and welded which are then ground smooth. All hardware is plated and each compartment shall have hinged doors which shall be external panel mounted to the door and to the enclosure. The door is removable from the open position. All doors have stop latches and "Eberhard" or equal door locks and handles with 3-point latches. Enclosure is rated NEMA 3R equivalent, which protects the regulators and switches from rain and weather.

Unless to difficult to ship, the units shall be factory assembled. When shipped, units are wrapped in cardboard sheeting then plastic wrapped for weather resistance. Units are then placed on a wooden pallet for easy lifting from the bottom. If lifting from the bottom is not desired unit may be lifted by the lifting lugs. Lifting lugs are located at the base where lifting plates may be attached for lifting by crane. Lifting attachments are not provided and must be supplied by others.

Each unit is provided with an Operating and Maintenance Manual to allow users to perform scheduled maintenance and to preserve the life of their enclosure.

NEMA 3R – Enclosures constructed for either indoor or outdoor use to provide a degree of protection to personnel against incidental contact with the enclosed equipment; to provide a degree of protection against falling dirt, rain, sleet, and snow; and that will be undamaged by the external formation of ice on the enclosure.

Paint Colors

Many colors are available which include ANSI 61 Gray, ANSI 70 Gray and Munsell Green to name a few. Paint colors can even be matched to existing units given the color number or paint chip.

Alesta®2 brand Powder Coating system is used to provide a tough, durable and highly decorative finish on regulator enclosure assemblies. The final product has a cured film thickness of approximately 2.5 to 3.0 mils and is volatile organic compound (VOC) free. For extremely corrosive environments, an additional primer coat is offered as an adder.

This is a superior system to other standard paint systems and has excellent hardness, flexibility, exterior durability, corrosion resistance, and chemical /solvent resistance.

Our factory employs a five stage pretreatment process that cleans, treats and seals the material to be coated, ensuring a quality, corrosion resistant finish. This process first thoroughly cleans the steel and then treats it with an Iron Phosphate conversion coating that serves as a rust inhibitor and bonding agent for the Powder Coating. The final step in this process enhances the corrosion resistance of the painted part as well as increasing the adhesion properties of the topcoat. All five steps work together to ensure a superior finish.

Alesta® brand powders is UL recognized for steel enclosures for outdoor use.


Penta Head Door Handles
Hex Head Door Handles
-B2G (GPO-3 Fiberglass) 40" Hinged Door Barrier
-B2L (Lexan1 brand) 40" Hinged Door Barrier
-L2G (GPO-3 Fiberglass) 40" Lift-out Door Barrier
-L2L (Lexan1 brand) 40" Lift-out Door Barrier
-W# (number of doors with) Window for Door
-NV No Venting
There are many ways to customize your order in lieu of different sizes. Items such as protective barriers behind each door, penta head door handles, dead front, live front, etc. Since different needs require different enclosures, table 1 below is a list of options that may guide you in constructing you own custom enclosure.

The first two options in table 1 are door handles. Standard Eberhard door handles are provided unless replaced by these options. The following four options are protective barriers. Utilities, electric companies, and REA sometimes require these protective barriers, which are located directly behind the door. All barriers are Nema and IEEE compliant.

The final two options are windows in the doors and no venting. If ordering a window in the doors please specify how many doors must have windows in them by adding a number immediately after the –W. 
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