Case Analysis: Distribution Network Voltage related power quality issues in a food and beverage industry

Published On: Dec 01, 2016


In today’s scenario, voltage related power quality (PQ) issues are quite common and faced by most of the industries. Voltage sags/swells and interruptions are some of power quality issues that can have severe financial impact on industries. Many times, these PQ issues are not taken seriously by industries and end up paying a heavy price for the same. This blog depicts one such example of a leading beverage manufacturing industry facing PQ issues.

Coca Cola, one of the leading beverage manufacturing companies in the world, grew over the years to become leader in non-alcoholic beverages. Since its inception in the year 1892, it adopted the best available manufacturing processes and now its plants across the globe have most modern and automated manufacturing lines.

The plant under was facing frequent PQ issues and other electrical network issues, thereby causing production loss. In order to protect its failures and loss of productivity, the plant undertook PQ study. Based on its finding, the plant team took essential steps to reduce the impact of power quality issues.

KEY ISSUES FACED BY PLANT DUE TO POOR PQ

Hindustan Coca Cola Beverages Pvt. Ltd (HCCB) Plant in Khurda Industrial Estate is one of the largest and key bottling facilities in Company Owned Bottling Operations (CBO) with 2400bpm+ manufacturing capacity, supported by 6 lines. For the last few years, Khurda Industrial estate has been experiencing poor quality of incoming power from State Electricity Board and all major industries (including HCCB) in this estate have been impacted badly due to this issue.

The plant was facing problem of stoppage of production line causing loss of productivity. The problems were mainly due to interruptions in power supply and under voltage events. Apart from this, plant was also facing problems due to over voltage particularly failure of electronic cards. After each power supply interruption, there was some time required to resume productivity varying from 10-15 minute. Table – 1 shows monetary loss faced by plant due to each event of supply interruption.

Sr. No.

Line

Line running time after power resume in mins

Production Capacity per hour (No of cases per hour)

Load factor

Actual Cases Lost

Monetary Loss in Rs. per event

1

Krones

15

1500

80%

300

3168

2

Maaza

12

1500

80%

240

2534.4

3

RGB

10

1500

80%

200

2112

4

Kinley

10

300

80%

40

422.4

5

PET-140

15

933

80%

187

1970.49

 

 

Total Loss

 

 

10207

Table 1. Monetary loss due to power supply interruption

The power supply interruptions were observed for 4 months, indicating the total number of occurrences. (See below table)

Month

Unscheduled Power cut

Unbalanced Voltage

Total No of Occurrences

 

No. of Occurrences

No. of Occurrences

January’14

10

9

19

February’14

17

8

25

March’14

45

42

87

April’14

68

51

119

Table 2. Power supply interruptions in each month

It can be seen that from January to April 2014, number of unbalanced voltage and unscheduled power supply interruptions were 250. With cost of each event being INR 10,207, plant lost around INR 25,51,750 (INR 25.51 lakhs) during the same period. Apart from loss in productivity, the plant also spent more money for operating DG sets due to each event which increased energy cost along with Green House Gas emission. The increased use of DG was not due to non-availability of power but due to poor quality of supply power. Thereupon, the plant was forced to use DG set despite availability of power.

Another major issue was faced when traction load was supplied from 33 kV industry feeder. The plant received its supply from 132 kV grid and stepped down to 33 kV at utility sub-station. The same 33 kV grid also supplies to traction load during maintenance or breakdown at dedicated grid of traction. When traction load is on the industry grid of 33 kV and electrical rail comes in operation, there are frequent changes in the operating condition. Due to sudden change in high loads, voltage across the grid and downstream of the grid gets affected. The loaded phase experiences serious under voltage & rapid variations. Traction load introduced 2nd, 3rd & 5th harmonics and under unfavourable conditions causing voltage amplification. Hence, due to frequent change in load and various trains operating at a given time, there is huge load variation on the grid thereby affecting all industries connected on the same grid.

Impact on Business

All above issues were affecting the business resulting in loss of productivity and service quality. Various effects of poor PQ that has direct impact on profitability of business are:

  • Electronics Failures resulting in increased downtime
  • Additional purchase of costly tools resulting in increased M/C tools
  • Environmental pollution

The plant was losing around INR 62.5 Million per year due to higher energy cost and loss in productivity. Also, around 180 tonnes of additional GHG is being released to atmosphere due to use of diesel in DG sets.

ASSESSMENT AND MEASUREMENT OF PQ ISSUES

In order to find a reliable solution during the un-scheduled power interruptions and voltage variations, the plant team carried out a detailed Power Quality Audit study to find reason of voltage variations and possible solution to mitigate the problem.

Summary of PQ Audit

The plant carried out a detailed power quality audit to find root cause of the problem. Measurements were carried out at all critical locations and logged for longer duration of time to record number of events and duration of each event. During the audit, measurements were carried out at following points.

Sr. No.

Measurement Point

1

33 kV main HT incomer

2

2000 kVA transformer – LT side

3

3150 kVA transformer – LT side

4

Krone UPS

In addition to above major locations, measurements were carried out at all load end MCC’s, UPS and servo stabilizer. Measurement analysis was carried out to study the voltage profile of transformers for different ratings, total harmonic distortions and power profile at the output of the UPS. Measurement result showed that there could be problem for the equipment installed at the plant due to current harmonics and voltage variations. However, further analysis was carried out to find if voltage variations are safe or unsafe for electronic components at the plant. It was seen that there is negligible variation in voltage profile at the output of UPS. Even though there are variation in the supply voltage more than 10 %, there is negligible (0.1%) variation in voltage profile at the output of the UPS.

MITIGATION TECHNIQUES USED FOR PQ ISSUES

The aforementioned issues being frequent and quite common with regular occurrence, the plant took various measures like installing SCADA system, forward and reverse synchronisation system, and Automatic Switch over system for DG sets during power failure.

  • Grid synchronization with the help of DG sets: During forward synchronization, DG’s are switched on half an hour before schedule power interruption. Before scheduled power interruptions, load is switched over to DG sets. During reverse synchronization DG sets are kept running even after power from the grid resumes. Once the system is synchronized, then load is transferred from DG set to grid power without any disturbance to the manufacturing process.

  • Use of SCADA system: SCADA system helped the operation team to monitor the voltage profile more closely. After installation of SCADA system, plant team could identify cause of malfunctioning of various sensitive equipment. They noticed voltage drops to as low as 15-20 Volts on the LT side for couple of milli seconds.

The plant has installed SCADA system to record severe voltage dips. The protection settings had to be adjusted and reason for these 2ms duration dips identified. Interruption records were alarming, as much as 60 times in some months. Hence, an auto changeover of supply through RMUs was thought be a solution, provided an alternate supply was available. The plant team also decided to install two UPS each of 600 kVA at critical locations to avoid breakdown arising due to voltage variations and un-scheduled power interruptions. Moreover, to mitigate the PQ issue due to change in traction load the plant requested state electricity DISCOM to separate traction load from industrial supply. It was also suggested that the traction load should be provided with an SVC with load balancing features but it was estimated to be an expensive solution.

Power Quality Blog

CONCLUSION

The mentioned case study is an example of ‘how poor quality power supply’ can affect a running industry and be counterproductive to industrial growth. From the measurement and analysis of the voltage variation, sags, over voltage and interruptions, it was evident that voltage fluctuations, over voltages, voltage sags and interruptions due to un-scheduled power cuts were main reason for the failure of critical components in the plant. Even servo stabilizer was not able to control the issues and there was variation in the output voltage of the servo stabilizer. Hence, this assessment facilitated plant team in mapping PQ issues and possible solution to mitigate the problem.

REFERENCES

  1. Distribution Network Voltage related power quality issues in a food and beverage industry

(This blog is based on a APQI case study titled “Distribution Network Voltage related power quality issues in a food and beverage industry”. It depicts the case of a unit/plant facing power quality issues due to internal and external factors and highlights various mitigation techniques adopted by the unit to mitigate these issues.)

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