30-09-2016, 10:42 AM
DESIGNING & DEVELOPING OFAN ELECTRO-MECHANICAL ACTUATOR FOR LIFE TESTING OF SWITCHGEARS WITH LARSEN & TOUBRO
1456978826-AprojectreportonBEproject.docx (Size: 2.21 MB / Downloads: 8)
Abstract
Switchgears are the switching devices that form the backbone of modern electrical distribution systems. In an electric power system, switchgear is the combinations of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply. One of the basic functions of switchgear is protection, which is interruption of short-circuit and overload fault currents while maintaining service to unaffected circuits. Switchgear also provides isolation of circuits from power supplies. To help ensure safe operation sequences of switchgear, trapped key interlocking provides predefined scenarios of operation. For example, if only one of two sources of supply is permitted to be connected at a given time, the interlock scheme may require that the first switch must be opened to release a key that will allow closing the second switch. Complex schemes are possible.Indoor switchgear can also be type tested for internal arc containment (e.g., IEC 62271-200). They are also inspected for their life i.e. the number of times switchgear can be turned ON and OFF (switching cycle). The project deals with the development of a machine which can be used to test the Life of the switchgears in the similar working environment.
INTRODUCTION
The Electrical & Automation Independent Company (EAIC) of L&T is one of the divisions involved in the design, manufacture and marketing of a comprehensive range of low voltage switchgear and other electrical and electronic products in areas of automation, energy management and medical equipment.
L&T is India’s largest manufacturer of low voltage switchgear & control gear as well as petrol metering & dispensing pumps which functions as The Electrical Group, earlier known as Group III, handles these functions, an independent profit centre within the corporate ambit of L & T. The group manufacturing facilities are located at Powai, Ahmednagar and Faridabad.
The Switchgear Testing Laboratory in their Powai campus has the following four stations-
1. Short Circuit Lab
2. Electrical Endurance Test Section
3. Thermal Lab
4. Mechanical Endurance Testing Lab
The Mechanical Endurance Testing Lab is the place where we are carrying out our proposed Project. There are various sections in this lab viz.
i)Mechanical Endurance
ii) Environmental laboratory
iii) Switchgear Design and Development Centre(SDDC)
iv) Calibration Centre
v) EMC HV Section
The sole purpose of the project is to make a suitable and economicalmachine to test the Number of Times a MCCB can turn ON and OFF i.e. the life of the MCCB. The system should have the similar operations but have the running cost minimum and as low as possible. The coming chapters will explain in detail the process of selection and design of a system for the Life Testing machine.
CURRENT SCENARIO: WHY TO TRY SOMETHING ELSE?
THE PNEUMATIC SYSTEM:
The current system under working which is used for testing the Life and the Mechanical Endurance of the MCCB’s is a Pneumatic actuator system governed by PLC.
STUDY OF ALTERNATIVES
The disadvantages of the pneumatic system rolled the wheel to think about the possible alternative solutions for obtaining the same motion with same or even greater accuracy and eliminating all the limitations of pneumatic system with greater control and lesser need of the human attention.
The below given are the possible alternatives that we studied and suggested for replacement of the existing system.
a) Servo Systems
Based upon the working principle and the motion of the required systems the Servo systems is the best candidate with the following economic point of view-
Investment
1. Servo Motor + Drive
• Initial Cost – 1.5x10=15 Lac
• Maintenance – Minimal
2. Servo Controller
• Initial Cost -1 Lac
• Maintenance – Minimal
3. PLC / Timer
• Initial cost – 10000x10=1 Lac
• Maintenance - Minimal
4. Coupling shaft
• Initial Cost – 1 Lac
• Maintenance – Minimal
ADVANTAGES:
1. Smooth power and reliable operation
2. Efficient control over the system parameters
DISADVANTAGES:
1. Very Costly both in fixed and running costs
2. Initial cost of the setup is also very high
3. Maintenance needs to be done frequently
4. Skilled operators are required
CONCLUSION: Thus we see that the Servo Systems do provide a good alternative but they are very costly which eliminates the very requirement of the project to be economical
Reversible AC Synchronous System
The Reversible AC Synchronous System incorporating the AC Induction Motor was considered here as the second alternative for obtaining the similar motion as that required.
The following costs were associated with this system-
Investment
1. AC reversible Synchronous Motor
• Initial Cost – 5000x10=50000
• Maintenance – Minimal
2. Drive - Not required
3. Controller
• PLC/Timer
Cost 10000*10 -1 Lac
4. Coupling shaft
• Initial Cost – 1 Lac
• Maintenance – None
5. Gear System
• Rack & Pinion (In-house design)
ADVANTAGES:
1. The suitability of the AC motor to the working environment is high
2. The operation is simple and easily controlled using a PLC.
3. The range of cost is within acceptable limits.
DISADVANTAGES:
1. The AC motors suffers from the ill effects of the inertia loading.
2. The losses in the current due to hysteresis is significant
3. The maintenance of the system needs to be done frequently.
CONCLUSION: Thus we see that the Reversible AC Synchronous System has cost compatibility but does not satisfy the accurate motion control needs. Hence it cannot be used for the new system.