Automation of Electrical Isolators/ Disconnector using Electrical Motor and Gearbox

GRD Journals- Global Research and Development Journal for Engineering | Volume 2 | Issue 4 | March 2017 ISSN: 2455-5703

Automation of Electrical Isolators/Disconnectors using Electric Motor and Gearbox Yash Abhang Student Department of Mechanical Engineering NBN Sinhgad School of Engineering Anuj Kadam Student Department of Mechanical Engineering NBN Sinhgad School of Engineering

Anas Qureshi Student Department of Mechanical Engineering NBN Sinhgad School of Engineering

Swapnil Kale Student Department of Mechanical Engineering NBN Sinhgad School of Engineering

Digvijay Mahajan Assistant Professor Department of Mechanical Engineering NBN Sinhgad School of Engineering

Abstract Electrical Isolators have been used primarily before circuit breakers in a power transmission substation. Circuit Breakers are used to isolate the circuit. The break points cannot be viewed externally as they lie within the circuit breaker. Electrical Isolators are therefore physical switches that are in place to ensure that the complete connection or disconnection to the whole circuit is made.

It is very essential safety switch. These Electrical Isolators used in substations are manually handled, to open or close the Electrical Isolator/ Disconnector switch. This process is hazardous for the person operating the Isolators/ Disconnectors. Therefore, to automate the operation an electric motor can be used. This motor can be used to operate the Electrical Isolator/Disconnector switch remotely. A gear box needs to be designed to give necessary output speed needed to operate the electrical Isolator/Disconnector switch mechanism. Hence, in this project a speed reducer gearbox has been designed for two electrical motors with powers: 0.5 HP and 1 HP. The gearbox uses spur gear pair and worm gear pair to get the necessary output speed.

Keywords- Electrical Isolator/Disconnector, Switch, Automation, Gearbox, Electric Motor

I. INTRODUCTION Electrical Isolators/Disconnectors are mechanical switches used to isolate the power transmission circuit. It is an important safety measure taken when there is any maintenance work taking place on the power lines. Circuit breakers are also used to disconnect the circuit. The circuit breakers have the disconnecting mechanisms inside the enclosure, therefore they cannot be seen from outside as the connectors are submerged in oil or gas. Thus, to ensure that the circuit remains truly disconnected another switch mechanism called electrical isolators/disconnectors are used. These isolators come in different types as per the number of breaks. Hence, they are aptly called 1) Single break Isolators, 2) Double break Isolators, 3) Pantograph Isolators. These Isolators are used both before and after the circuit breaker to ensure proper safety, and enables maintenance of the circuit breaker. It can be hence said that Isolator is a type of mechanical switch that is manually controlled to connect or disconnect the electrical circuit.

Isolators/Disconnectors switches are not provided with any arc quenching mechanism thus they need to be operated only when the circuit breaker is open. If an isolator is opened in a live circuit it may cause huge electrical arcs which would be very hazardous. Hence, they are operated only after making sure that circuit breaker is open and passing no current. Furthermore, the Isolator/Disconnector switch mechanism are handled manually. Manual handling of the mechanism requires a person to go inside the substation and open/close the Isolator/Disconnector switch by rotating the handle actuating the complete mechanism. This may be considered safe in low voltage substations, but in substations more than 220 KV or above it is extremely dangerous to control the electrical Isolators/Disconnectors switches manually. Therefore, remote control and automation of these switches is necessary.

This project thus uses motor as an actuator for the mechanism, although the motor cannot be directly connected to the electrical Isolator/Disconnector mechanism as the output rpm is very high. Hence, we have designed a speed reducer gearbox which reduces the high motor RPM to optimum RPM needed for actuating the mechanism.

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Automation of Electrical Isolators/Disconnectors using Electric Motor and Gearbox (GRDJE/ Volume 2 / Issue 4 / 012)

Double Break Isolator Single Break Isolator Fig. 1: Types of Electrical Isolators/ Disconnectors

II. PRINCIPLE The automation of electrical Isolators/Disconnectors requires an electric motor and gearbox. Therefore, we need to select an electric motor and design a speed reducer gearbox for the respective motor. The manual mechanism is to be replaced and substituted with an automatic actuator. The gearbox should approximately operate on a load of 15Kg. The whole mechanism is a kinematic chain initiated by the actuator. The output from the gearbox should be approximately around 2-3 RPM for the mechanism to operate.

Higher torque is needed initiate the mechanism.

Fig. 2: Isolator Mechanism

III. METHODOLOGY The motor used in the project is of very low power 0.5HP and 1 HP as a low RPM motor would be effective. The gearbox used here is a two-stage gearbox with reduction of 13:1 and 52:1 in respective stages. The gear pair used are spur gear pair and worm gear pair.

The spur gears have following advantages: 1) Easy to manufacture 2) Comparatively cheap 3) Have highest efficiency 4) Used for low speed and load application The worm gear pair used next is because of high speed reduction it provides. Therefor the advantages of using worm gear pairs are: 1) A high-speed reduction ratio compared to other gear pairs.

2) Worm gear drives are compact in size (Overall dimensions) compared to spur and helical gear pairs.

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Automation of Electrical Isolators/Disconnectors using Electric Motor and Gearbox (GRDJE/ Volume 2 / Issue 4 / 012)

3) Smooth and silent working.

4) Self-locking can be enabled if only motion is transmitted from worm to worm wheel.

The gearbox uses grease for lubrication to provide smooth operation. The gears are manufactured by gear hobbling process.

Stepped shafts are used for better fitting and balancing of gears, these were designed using ASME code method.

Fig. 3: Worm Shaft

Fig. 4: Worm Wheel

IV. DESIGN A. Gearbox Components and Design 1) Spur Pinion: The material used for manufacturing of spur pinion is 45C8 with 20ยบ pressure angle, this is coupled to the electric motor.

2) Spur Gear: The material used for manufacturing is same as that of pinion i.e. 45C8 with 20ยบ pressure angle, this mounted on the worm shaft.

3) Worm: Worm used is manufactured using 45C8 material, which is driven by the spur gear mounted on the shaft.

4) Worm Gear: Worm gear is manufactured using 45C8 material with nitriding and phosphor bronze.

5) Casing: This manufactured using cast iron to provide adequate strength and damping vibration.

6) Output Shaft: Stepped shaft is manufactured using 45C8, material saving is obtained by making stepped shaft.

7) Bearing: Bearing selected are ball bearing to balance axial thrust in all directions.

B. Parameters of Shaft Design 1) Worm Shaft Diameter = 30mm 2) Output Shaft Diameter =35mm C. Selection of Bearing 1) Ball Bearings (6204 Z2)

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Automation of Electrical Isolators/Disconnectors using Electric Motor and Gearbox (GRDJE/ Volume 2 / Issue 4 / 012)

D. 1) 2) 3) 4)

Electric Motor Specifications Power- 0.5 HP Current- 1.2A RPM- 1365 Efficiency – 66% Table 1: Design Parameters of Spur Gear Pair Parameters Spur Gear Spur Pinion Face width = 12 m

18mm

18mm

Addendum = m

1.5mm

1.5mm

Dedendum = 1.25m

1.875mm

1.875mm

Clearance = 0.25m

0.375mm

0.375mm

Diameter 195mm 15mm Table 2: Design Parameters of Worm Gear Pair Parameters Worm Worm Gear Addendum

2.5mm

2.5mm

Dedendum

3.125mm

3.125mm

Tooth Height

5.63mm

5.63mm

Diameter

30mm

130mm

V. CONCLUSION The electrical Isolators/ Disconnector once automated can be directly controlled remotely from a central location. This enables better power grid control and distribution of power according to the demand. The high voltage substations can now be operated with maximum safety. The use of Motor and gearbox mechanism is not very expensive and can be implemented without any major rise in cost.

ACKNOWLEDGMENT It gives us great pleasure to present our project “Automation of Electrical Isolators/ Disconnectors using Electric Motor and Gearbox”. This project could not be initiated without support of our esteemed guide Prof. Digvijay Mahajan who provided his valuable inputs and expertise of Machine Design. We also appreciate all the people who worked as a team and gave us critical assistance and resources to ensure completion of this paper.

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Modeling and robust control of worm-gear driven systems,T.-J. Yeh *, Feng-Kung Wu in Simulation Modelling Practice and Theory 17 (2009) 767–777 Study on interactions between tooth backlash and journal bearing clearance nonlinearity in spur gear pair system Zhenxing Liu, Zhansheng Liu, Jingming Zhao, Guanghui Zhang in Mechanism and Machine Theory 107 (2017) 229–245 Study of the efficiency of spur gears made of powder metallurgy materials – ground versus super-finished surfaces Xinmin Li n, Mario Sosa, Martin Andersson, Ulf Olofsson Clauser, H. R., Industrial and Engineering Materials, McGraw Hill, 1975 Dieter, G. E., Engineering Design- A Materials and Processing Approach, McGraw Hill, 1987 V. B. Bhandari, “Engineering Materials” in Design of Machine Elements, 4th ed. McGraw Hill Education.

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