Gas Insulated Substations (GIS)

 

High Voltage Gas Insulated Substations (GIS) are one-time installations having a very long operating life with minimal maintenance, unlike Air Insulated Substations (AIS). However, being a complex and high-cost construction, the operation and maintenance of GIS is still an elusive topic that requires a closely coordinated plan and schedule based on the manuals and instructions of OEMs.

They draw a lot of similarities, as well as quite a few differences from their conventional counterpart, AIS.

After its inception in the mid-1960s, GIS technology has become a remarkable success over a wide range of high voltage applications up to 800 kV. Reliable operation and compact size have been its main advantages over its conventional air-insulated counterparts. Despite a very high initial capital cost, these two advantages reflect in other multiple aspects like low maintenance, minimum footprint, enhanced safety, pleasing aesthetics, and so on.

Operating a GIS module could be a challenge for untrained operators because of completely encapsulated switchgear, measuring equipment, and conducting parts. Although the components and operations are principally similar to an AIS, the physical arrangement of those elements marks a notable difference.

The presence of metallic enclosure and unavailability of visible indication of component operations require getting used to. Furthermore, a GIS module requires stringent interlocking schemes between breakers, maintenance switches, and earthing switches to ensure safe operation and maintenance.

WORKING PRINCIPLE OF VFD

It is important to be familiar with the working principle of VFDs as they are extensively used in AC motor-driven applications. VFD has greater functionality and operation capabilities than conventional motor drives, which will be explained in detail in this article.

Let’s take a 3-phase load as an example to see how VFDs work. Firstly, when AC power is supplied from the mains, it directly passes through the first VFD stage – Rectifier stage. The current passes through six diodes that convert the AC-supplied current into DC. In short, each of the three phases is connected to one pair of diodes, which only allow the peak of each phase to pass through it.

Therefore, the output of the 3 phases passing through diodes, when measured by an oscilloscope.

the output current looks like a rough DC or just a current wave that doesn’t include the negative side of the current. Therefore, this current needs to be converted into a healthy DC and the best way to achieve that is by connecting a capacitor that will smooth the output current.

This capacitor is the VFD’s second stage, called the DC filter. Because of the charging and discharging effect of the capacitor, the current passing through the DC filter will have a wave.

After the DC is considered smooth, it is ready to pass through the third stage of the VFD – the IGBTs inverter to convert it into AC again. When the current reaches this stage, the converted AC’s frequency could be varied accordingly. The connected number of IGBTs here will be turned on and off very fast to produce an AC-like waveform that will run the connected motor as if it was connected directly to an AC supply.

The IGBTs here act like switches that when rapidly switched on and off, create the Pulse-Width Modulation (PWM) that is a key to allowing a VFD to control the speed of the motor.

Variable Frequency Drive (VFD)

 

For many years, the major challenge to some motor-driven applications was the inability to control their speed. However, the advent of reliable power electronics made it possible to control the speed of motors using variable-frequency drivers.

VFDs are widely used in many applications nowadays. The main reason is that they have greater functionality and operation capabilities compared to conventional motor drives when starting a motor.

The working of VFD is based on the control of frequency and voltage simultaneously through a PWM inverter, it is used to control the speed of AC motor-driven applications. In addition, variable frequency drives offer protections like phase, under, and overvoltage protection.

Components of VFD

To understand the working principle of a variable frequency driver, it is important to know what it is composed of. In other words, you need to know what leads the currents passing through a VFD of a 3-phase motor, for instance, to be changed from AC to DC and then back to AC again.

VFD comprises three main sections: Rectifier, Filters, and Inverter.

1. Rectifier: The first stage of VFD. It converts AC power fed from the mains to DC power. It mainly utilizes diodes that are connected in parallel to convert AC power into DC.
2. Filter: A capacitor that is used to smooth the rectified DC power.
3. Inverter: Transistors (IGBTs) used to work to be switched on and off rapidly to create a pulse-width modulation which creates an AC-like wave that will allow the VFD to control the speed of the motor.

"Why Do You Want To Work Here?"

 

"Why Do You Want To Work Here?"

The hiring manager is trying to get at your underlying motivations for wanting this job. Are you here just for a paycheck, or do you see yourself becoming an integral part of the company and growing along with it?

You need to show them that you want to become “part of the family.” At the same time, however, show how your “wants” coincide with their “needs.”

EXAMPLE ANSWER:

“One thing that really attracted me to your company and this opportunity is the company’s dedication to its local community. I’m a community-oriented person, both on and off the job. Along with preferring a work environment with an exceptional culture – such as the one your company offers – I value employers that look outside their walls for opportunities to make a difference. I feel your company does that to a degree you don’t typically see, and I want to be a part of a business like that.”

"What Is Your Greatest Strength?"

"What Is Your Greatest Strength?"

This is a fairly straightforward question to handle. Talk about a “strength” that you know the company puts a lot of value in.

EXAMPLE ANSWER:

“My biggest strength is my problem-solving capabilities. Generally, I’m a methodical person with exceptional research skills. However, I’m also comfortable thinking outside of the box. When taken together, that allows me to navigate the unknown with greater ease. I know how to track down the information I need, as well as how to look deeper, creating opportunities to innovate when I need solutions.”

"Why Should We Hire You?"

 

"Why Should We Hire You?"

This is another incredibly common question, and it gives you a great opportunity to stand out from the crowd and really show the hiring manager how you can help the company.

The key thing to remember here is: be specific.

Leverage your company research and the job description to find exactly why the company is hiring someone for this position. What problem/pain point does the new hire have to solve? You need to show that you are the perfect candidate that can solve those problems/pain points.

EXAMPLE ANSWER:

“After reviewing your job description, it was clear that finding someone with a willingness to learn that would face challenges head-on was a priority. Generally, I relish opportunities to explore the unknown, and I’m eager to glean all I can from those around me. Additionally, I understand the value of doing my own research to find answers, as well as asking intelligent questions of those around me. Taken together, I think that makes me an exceptional fit in that regard, making me an excellent candidate for the role.”

"Tell Me About Yourself..."

 

"Tell Me About Yourself..."

This classic opening question should probably be put out to pasture, but it’s still one of THE most common interview questions you’ll face. With that being said, it still seems to trip up a ton of job seekers every year.

EXAMPLE ANSWER:

“For the past five years, I’ve been working in a fast-paced nursing role in one of the area’s top hospitals. During that time, I’ve not only had the opportunity to learn from some of the leading specialists in their field, but I’ve also furthered my education.

“I’ve recently graduated with a nursing degree and have completed my initial licensing requirements. At this time, I am eager to take the next step in my career, allowing me to put my knowledge and experience to work in a challenging role.”

Electrical Testing Engineer Interview Questions and Answers

What are the most important skills of an electrical test engineer to have?

This question can help the interviewer determine if you have the skills and qualifications to succeed in this role. Use your answer to highlight your technical, communication and problem-solving skills.

Example: “The most important skill for an electrical test engineer is their ability to communicate effectively with others. Electrical engineers need to be able to clearly explain their ideas and concepts to other members of a team. I also think it’s important to have strong technical skills because they allow me to understand complex problems and develop solutions. Finally, I believe that being organized and detail-oriented are essential skills for electrical test engineers.”

Provide an example of a time when you had to work with a difficult or challenging customer.

Interviewers may ask this question to assess your customer service skills. They want to know how you handle conflict and whether or not you can resolve it in a professional manner. In your answer, try to focus on the steps you took to solve the problem and maintain a positive relationship with the customer.

Example: “In my previous role as an electrical test engineer, I had a difficult customer who would often call me at all hours of the day about issues they were having with our software. This made it challenging for me to get any work done because I was constantly answering their questions. Eventually, I scheduled a meeting with them to discuss the issue. We talked through some of the challenges they were having and came up with a solution that allowed them to use the software more effectively.”

If hired, what would be your priorities during your first few weeks on the job?

This question helps the interviewer determine how you plan to fit into their team and what your goals are for your first few weeks on the job. Your answer should include a list of things you would do to get acclimated to your new role, including meeting with coworkers and learning about company policies and procedures.

Example: “During my first week, I would want to meet as many people in the office as possible. I also plan to spend time getting familiar with the company’s computer systems and any other resources that will help me complete my work. I would also like to learn more about the projects we’re currently working on so I can contribute to them from day one.”

What makes you the best candidate for this electrical test engineer position?

This question is your opportunity to show the interviewer that you are qualified for this role. Use examples from your experience and education to highlight your skills, knowledge and abilities.

Example: “I have a bachelor’s degree in electrical engineering technology with an emphasis on software development. I also have five years of experience as an electrical test engineer at my current company where I’ve worked on projects like developing new products and testing them for safety. My background in both hardware and software development makes me well-suited for this position.”

Which electrical components or systems have you tested in the past?

This question can help the interviewer understand your experience level and how you apply it to a new role. Use examples from your resume or past projects to highlight your skills and abilities as an electrical test engineer.

Example: “In my last position, I tested all of the components in a power grid system that was used for a large-scale solar farm. The project required me to work with several other engineers to ensure we were testing each component correctly and efficiently. We also had to make sure our tests didn’t interfere with the operation of the entire solar farm. My knowledge of the different systems helped us complete the project on time.”

What do you think is the most challenging part of being an electrical test engineer?

This question can help interviewers understand what you think about your job and how it relates to the company. They may want to know that you enjoy working as an electrical test engineer, but they also might appreciate hearing about any challenges you’ve faced in this role. Consider discussing a challenge you have experienced and how you overcame it or plan to overcome it.

Example: “The most challenging part of being an electrical test engineer is finding ways to improve testing processes. I love my work because I get to solve problems every day, but sometimes it’s hard to find new solutions when we’re doing something over and over again. However, I try to look at each project with fresh eyes and consider different approaches.”

How often do you update your knowledge and skills as an electrical test engineer?

This question can help interviewers understand how you approach your career and whether you’re open to learning new things. Your answer should show that you are committed to continuous improvement, but it’s also important to mention specific ways you’ve done this in the past.

Example: “I am always looking for ways to improve my skills as an electrical test engineer. I have taken several online courses on topics like digital testing and automated testing. These courses helped me learn more about these processes and apply them to my work. In addition, I regularly read industry publications and attend conferences to stay up-to-date with current trends.”