September 19, 2008
Northport - Norwalk Harbor Cable (NNC)
Tie line
Technical Assessment of Operating up to NNC Inter Tie STE Ratings
Executive Summary
Three (3) 138kV submarine cable circuits (Lines 601, 602, and 603) have been installed from Northeast
Utilities’ (NU) Norwalk Harbor 6J Substation to Long Island Power Authorities’ (LIPA) Northport 6F
Substation to replace the existing single 138kV circuit. The new cables were put in service on July 29,
2008.
NNC single cable operation while switching has caused a concern with ISO-NE and the NYISO. The
switching method presently agreed upon involves switching one cable at a time, each cable requiring
approximately 45 minutes to properly operate disconnects, fuses and ground switches. The single cable
operation scenario has caused transaction cuts between New England and New York and poses system
reliability concerns.
In order to prevent single cable operation from causing transaction cuts or having emergency states
invoked, the NYISO is being requested to grant an exception to Normal Transfer Criteria and allow the
NNC tie line to be solved to the post contingency STE rating instead of the LTE rating (for any one
cable; 601, 602 or 603). Such an exception will benefit both ISOs as well as both Connecticut and New
York state electric customers.
Thermal and voltage analysis study results demonstrate that there will be no adverse impact on system
reliability as a result of granting the exception by the NYISO / NYSRC to allow any one NNC cable to
be solved to the post contingency STE rating instead of the LTE rating. Phase angle regulation
capability is available at Northport to reduce NNC loading to the NNC LTE rating within 15 minutes
without causing any other facility to be loaded beyond its LTE rating. Use of the STE rating rather than
the LTE rating provides for a consistent operating practice with ISO-NE.
References: New York State Reliability Council (NYSRC) Reliability Rule B-R1 and E-R1.
Study Assumptions
Study time period: Summer 2008
Load flow base case:
- Summer 2008 peak load case
- All lines in service
- LIPA imports from NYISO via Y49 and Y50 maximized
- 286 MW wheel to Jamaica
- Shoreham CSC set at 330 MW import to Long Island
- Neptune set at 660 MW import to Long Island
1
September 19, 2008
- NNC single cable operation thermal ratings: 155 / 192 / 430 MVA (normal / LTE / STE) for any
individual cable
- For reference: NNC three (3) cable operation thermal ratings for any individual cable: 100 / 112 / 175
MVA (norm / LTE / STE); respecting prior cables’ (#1385) thermal ratings
Norwalk Harbor 115/138kV Auto Transformer Data
- Thermal Ratings: 402/ 402/ 449 MVA (normal / LTE / STE)
- Impedance: assume the impedance of the new replacement auto (data provided by ISO-NE), as
this auto is scheduled for replacement in October/November 2008
Thermal and Voltage Technical Assessment
Two main load flow base cases were set up for this technical assessment. These cases represent the
bounds of flows for imports to and exports from LI at the present normal FERC scheduling limit of 100
MW.
-
-
Import to LI from CT
o Case 1 simulates a 100 MW flow from Connecticut to Long Island over the NNC inter
tie (single cable operation)
Export from LI to CT
o Case 2 simulates a 100 MW flow from Long Island to Connecticut over the NNC inter
tie (single cable operation)
To determine the impact of operating to the post contingency STE rating, a severe system contingency
was simulated for each of the above cases. For testing Long Island imports, case 1, the loss of the
Shoreham Cross Sound Cable (CSC) HVDC (loss of 330 MW) was simulated. For testing Long Island
exports, case 2, the loss of Millstone Unit #3 (loss of approximately 1200 MW) was simulated. Pre and
post contingency PSS/E load flow plots for a portion of the power system in the vicinity of Northport
(Long Island) and Norwalk Harbor (Connecticut) are provided in the attached Appendix for reference.
These plots summarize pre and post contingency line flows and bus voltages.
Discussion of Results
Case 1 - Import to LI of 100 MW
No normal overloads are observed in this case. Assuming operation to post contingency LTE ratings, the
following contingency overload(s) were observed:
Table 1
2008 Summer Peak Load Flow Analysis Results – NNC single cable operation
Pre-contingency flow = 100 MW to L.I.
PERCENT
Limiting Element
Loss of
LOADING
NNC (LTE = 192 MVA)
Shoreham CSC
115% of LTE
2
September 19, 2008
Since the post contingency flow is well below the single cable STE rating of 430 MVA, solving to the
STE rating will mitigate this overload. The Northport phase angle regulator (PAR) associated with NNC
is available to reduce NNC loading to the NNC LTE rating within 15 minutes without causing any other
facility to be loaded beyond its LTE rating.
No pre or post contingency voltage violations were detected.
Case 2 - Export to CT of 100 MW
No normal overloads are observed in this case. Assuming operation to post contingency LTE ratings, the
following contingency overload(s) were observed:
Table 2
2008 Summer Peak Load Flow Analysis Results – NNC single cable operation
Pre-contingency flow = 100 MW to CT.
PERCENT
Limiting Element
Loss of
LOADING
NNC (LTE = 192 MVA)
Millstone #3
128% of LTE
Since the post contingency flow is well below the single cable STE rating of 430 MVA, solving to the
STE rating will mitigate this overload. The Northport phase angle regulator (PAR) associated with NNC
is available to reduce NNC loading to the NNC LTE rating within 15 minutes without causing any other
facility to be loaded beyond its LTE rating.
No pre or post contingency voltage violations were detected.
Conclusions
This technical assessment demonstrates that there will be no adverse impact on system reliability as a
result of granting the exception by the NYISO / NYSRC to allow the NNC tie line to be solved to the
post contingency STE rating instead of the LTE rating (for any one cable; 601, 602 or 603). Phase angle
regulation capability is available at Northport to reduce NNC loading to the NNC LTE rating within 15
minutes without causing any other facility to be loaded beyond its LTE rating. For single cable
operation, it is expected that the maximum post contingency phase angle regulator adjustment will be on
the order of 50 to 60 MW.
3
September 19, 2008
This exception will not adversely impact existing transfer capabilities between New England and New
York and is expected to improve overall system reliability by:
- relieving existing restrictions on New York – New England transfer limits which may arise in
real time due to:
o loss of Millstone Unit #3
o loss of Pleasant Valley – Long Mountain 398 line
o loss of Shoreham CSC
o other NY or CT system contingencies
- mitigating the need for transaction curtailments
4
September 19, 2008
APPENDIX
NNC One Line Diagram
&
Pre and Post Contingency Load Flow Summary Plots
5
DRAFT
48.6R
129329
ELWOOD 2
1.035
119.0
103171
NWLK HAR
129027
NRTPTG4
102.5
251.7
254.3
250.0
46.6R
27.0
103169
RYTN J A
1
121.9
32.2
1.024
141.3
103168
GLNBROOK
43.3
1.024
141.3
250.0
112.4
254.7
53.7
252.1
SW
129026
NRTPTG3
140.6
28.7
35.2
109.0
35.0
123.8
132.7
185.0
CASE 1: NNC - one cable I/S
100 MW Import to LI
129342
NRTHPRT2
1
129328
ELWOOD 1
129024
NRTPTG1
103172
NORWALK
123.4
SW
35.2
0.0
316.2
250.0
249.8
251.2
24.5R
129343
NRTHPT P
369.0
73.5
72.3
373.9
369.1
73.6
72.3
250.1
251.5
140.8
69.3
68.5
63.5
64.2
31.4
31.6
103166
NORHR138
1.030
118.5
250.0
27.4R
1
373.0
139.9
NNC Inter tie (one cable I/S)
129025
NRTPTG2
129344
NRTHPT1
99.3
100.4
100.4
62.0
62.4
24.0
0.9937
71.7
1.0000
129355
PILGRIM
71.7
1.026
141.6
1
314.6
100.6
24.2
103237
ELYAVE
103173
SASCO CR
140.6
15.6
1.038
143.3
99.3
170.4
61.3R
1
205.7
33.4
34.9
67.5
67.5
1.034
118.9
103271
RYTN J B
112.0
103552
NORHAR#2
Bus - VOLTAGE (KV/PU)
Branch - MVA/% OF RATE A
Equipment - MW/MVAR
100.0%RATEA
1.050OV0.950UV
2.5
165.0
1.015
18.3
1.031
142.3
168.0
178.4
2
1.026
141.5
1.0530
159.0
60.0H
1.014
20.3
1.0530
67.7
207.3
1.025
117.9
1.0000
68.9
72.6
103551
NORHAR#1
1
172.5
69.4
21.4
1.033
142.5
174.6
1.0000
21.4
1.0000
99.1
1.0000
-7.70
53.7
172.9
154.9
155.8
63.2
63.8
1.035
119.0
103207
FLAX HIL
43.3
85.3
84.9
37.5
1.030
118.4
37.5
62.7
62.3
28.6
28.7
1.014
116.7
1.025
117.8
129026
NRTPTG3
107.1
129329
ELWOOD 2
44.4
1.035
119.0
103171
NWLK HAR
128.2
1.021
140.8
250.0
60% I
63.1R
25.8
257.8
117.3
254.4
N/A
103168
GLNBROOK
1
19.7
SW
25% I
24.6
36.4
133.2
185.0
CASE 1a: NNC - one cable I/S
Post Contingency loss of Shoreham CSC
129342
NRTHPRT2
106.3
129328
ELWOOD 1
129027
NRTPTG4
94.3
22% I
253.8
N/A
17.4
257.2
250.0
60% I
60.3R
103169
RYTN J A
1
117.1
21.6
1.021
140.9
103172
NORWALK
116.9
129024
NRTPTG1
26% I
SW
25.8
0.0
251.8
N/A
254.4
250.0
59% I
47.1R
106.7
65.7
N/A
255.2
252.6
N/A
64.7
432.3
250.0
59% I
51.4R
78.1
30% I
30.1
36% I
103166
NORHR138
1.030
118.5
N/A
427.5
222.8
64.7
113.3
66% I
65.8
30.0
NNC Inter tie (one cable I/S)
1
427.6
66% I
79.1
38.6
37.8
129025
NRTPTG2
431.4
108.7
39% I
129343
NRTHPT P
228.1
228.1
114.9
54.9
115% I
129344
NRTHPT1
N/A
0.9937
61.4
1
334.9
1.0000
129355
PILGRIM
333.9
61% I
61.4
1.023
141.2
44
229.7
55% I
55.2
%
I
103237
ELYAVE
103173
SASCO CR
128.1
N/A
15.6
40% I
40.3
1.0000
223.2
1.0000
-7.70
1.034
142.7
222.8
125.6
250.1
46.2
63.3
46% I
63.3
1.024
117.8
103551
NORHAR#1
199.8
178.0
N/A
1.0530
159.0
102% I
80.0H
1.0000
1
60.1
1.034
118.9
170.6
103271
RYTN J B
105.9
1.025
18.5
1.026
141.6
103552
NORHAR#2
Bus - VOLTAGE (KV/PU)
Branch - MVA/% OF RATE B
Equipment - MW/MVAR
178.4
N/A
1.014
20.3
1.0530
168.0
102% I
60.0H
1.0000
100.0%RATEB
1.050OV0.950UV
123.8
122.0
103207
FLAX HIL
36.5
80.0
40% I
2
1.020
140.7
2.5
63% I
45.3
61% I
61.1
247.8
40.3
1.024
141.3
201.9
123.2
1
44.4
172.9
38.9
79.4
31% I
39.7
85.0
84.6
30.5
30.6
29% I
1.035
119.0
29.1
1.030
118.4
1.013
116.5
29.1
1.024
117.7
129026
NRTPTG3
116.2
129329
ELWOOD 2
45.5
1.035
119.0
103171
NWLK HAR
131.3
1.021
140.8
250.0
60% I
63.5R
25.9
257.9
117.7
254.5
N/A
103168
GLNBROOK
1
21.4
SW
26% I
25.9
36.6
140.4
185.0
129342
NRTHPRT2
106.7
129328
ELWOOD 1
CASE 1b: NNC - one cable I/S
Post Contingency loss of Shoreham CSC
NNC flow reduced to LTE rating
129027
NRTPTG4
102.4
23% I
253.8
N/A
18.9
257.2
250.0
60% I
60.6R
103169
RYTN J A
1
123.8
22.8
1.021
140.9
103172
NORWALK
117.3
26% I
129024
NRTPTG1
SW
25.9
0.0
313.9
116.9
62.8
N/A
255.6
252.9
N/A
61.6
413.2
250.0
59% I
53.0R
103166
NORHR138
406.6
191.2
61.6
97.2
63% I
63.0
75.0
29% I
28.9
1.030
118.5
N/A
1
406.7
63% I
28.8
NNC Inter tie (one cable I/S)
129025
NRTPTG2
412.2
76.0
42.2
41.4
37% I
254.7
118.5
42% I
129343
NRTHPT P
195.2
195.2
98.3
46.9
98% I
129344
NRTHPT1
N/A
0.9937
252.0
N/A
250.0
59% I
48.7R
1.0000
57.5
1
129355
PILGRIM
313.0
58% I
57.5
1.023
141.1
45
196.5
47% I
47.2
%
I
103237
ELYAVE
103173
SASCO CR
131.2
N/A
15.6
35% I
34.5
1.0000
191.3
1.0000
-12.79
1.035
142.8
191.2
116.0
243.4
42.7
61.6
43% I
61.7
1.024
117.8
103551
NORHAR#1
190.0
178.0
N/A
1.0530
159.0
102% I
80.0H
1.0000
1
57.2
1.034
118.9
170.6
103271
RYTN J B
106.3
1.025
18.5
1.026
141.5
103552
NORHAR#2
Bus - VOLTAGE (KV/PU)
Branch - MVA/% OF RATE B
Equipment - MW/MVAR
178.4
N/A
1.014
20.3
1.0530
168.0
102% I
60.0H
1.0000
100.0%RATEB
1.050OV0.950UV
133.7
132.2
103207
FLAX HIL
36.6
74.3
43% I
2
1.019
140.6
2.5
62% I
41.7
58% I
58.4
241.2
34.5
1.025
141.5
193.0
113.5
1
45.5
172.9
42.2
73.7
28% I
42.9
85.5
85.1
28.3
28.4
29% I
1.035
119.0
29.2
1.030
118.4
1.013
116.5
29.3
1.024
117.7
300.0
129027
NRTPTG4
145.4
300.9
38.3
304.0
300.0
49.4R
103169
RYTN J A
1
158.4
41.8
1.024
141.3
1.035
119.0
103171
NWLK HAR
44.8
51.2R
129329
ELWOOD 2
103168
GLNBROOK
116.4
304.3
60.8
301.1
1.023
141.2
SW
129026
NRTPTG3
159.3
40.8
36.4
154.9
45.2
128.2
171.2
185.0
CASE 2: NNC - one cable I/S
100 MW EXPORT to CT
129342
NRTHPRT2
1
129328
ELWOOD 1
129024
NRTPTG1
103172
NORWALK
127.8
SW
36.5
0.0
315.1
300.0
71.5
29.7R
129343
NRTHPT P
64.6
335.5
329.7
66.1
64.6
301.8
299.9
94.9
43.6
43.7
1.031
118.5
300.0
33.0R
129344
NRTHPT1
98.4
99.7
99.7
61.5
62.8
24.2
1.0187
65.9
96.2
93.0
1
329.6
204.1
92.7
103166
NORHR138
129025
NRTPTG2
334.4
204.3
NNC Inter tie (one cable I/S)
301.5
299.6
1.0000
129355
PILGRIM
71.5
1.026
141.5
1
313.8
98.9
23.8
103237
ELYAVE
103173
SASCO CR
159.2
15.6
1.024
141.4
98.4
164.4
41.9R
1
160.1
10.7
13.6
52.5
52.5
1.034
118.9
103271
RYTN J B
116.0
103552
NORHAR#2
Bus - VOLTAGE (KV/PU)
Branch - MVA/% OF RATE A
Equipment - MW/MVAR
100.0%RATEA
1.050OV0.950UV
2.5
160.8
1.005
18.1
1.030
142.2
168.0
173.1
2
1.025
141.5
1.0530
159.0
41.9R
1.004
20.1
1.0530
60.5
1.0000
61.8
161.2
103551
NORHAR#1
1
154.1
28.3
1.026
118.0
1.031
142.3
156.6
22.3
21.2
1.0000
21.2
1.0000
98.3
1.0000
-17.09
60.9
169.4
218.6
218.4
89.1
89.5
1.035
119.0
103207
FLAX HIL
44.9
121.9
53.6
1.030
118.5
121.3
78.1
77.5
35.6
35.7
1.015
116.7
53.6
1.025
117.9
129026
NRTPTG3
136.0
129329
ELWOOD 2
1.035
119.0
103171
NWLK HAR
60.3
300.0
71% I
52.2R
174.1
1.023
141.2
30.9
304.5
140.2
301.2
N/A
103168
GLNBROOK
1
25.0
SW
29% I
28.5
43.8
154.9
185.0
CASE 2a: NNC - one cable I/S
Post Contingency loss of Millstone #3
129342
NRTHPRT2
127.8
129328
ELWOOD 1
129027
NRTPTG4
125.5
26% I
300.9
N/A
23.0
304.2
300.0
71% I
50.3R
103169
RYTN J A
1
141.0
25.9
1.024
141.3
129024
NRTPTG1
103172
NORWALK
139.8
31% I
SW
30.9
0.0
300.0
70% I
27.7R
241.1
43.4
113.1
43% I
103166
NORHR138
129025
NRTPTG2
43.5
1.031
118.5
284.3
44.2
293.1
N/A 299.8
42.8
N/A
301.6
284.3
300.0
70% I
30.9R
N/A
255.6
44% I
44.4
249.4
128% I
42.8
128.5
129344
NRTHPT1
N/A
126.7
249.4
61% I
60.5
1.0187
44% I
1
291.9
114.6
85.5
85.4
NNC Inter tie (one cable I/S)
301.3
299.5
N/A
240.6
86% I
129343
NRTHPT P
44% I
65.3
1
358.3
1.0000
129355
PILGRIM
356.5
65% I
65.3
1.025
141.5
60
247.1
59.4
%
I
103237
ELYAVE
103173
SASCO CR
174.0
N/A
15.6
46% I
45.7
1.0000
254.2
1.0000
-17.09
78.3
28.4
28.8
25.6
25.6
1.027
118.2
132.9
168.0
N/A
1.0530
159.0
96% I
54.2R
1.0000
1
39.8
1.034
118.9
163.2
103271
RYTN J B
127.3
1.011
18.2
1.031
142.2
103552
NORHAR#2
Bus - VOLTAGE (KV/PU)
Branch - MVA/% OF RATE B
Equipment - MW/MVAR
254.2
254.8
103207
FLAX HIL
43.8
95.2
176.5
N/A
1.011
20.2
1.0530
81% I
168.0
101% I
54.2R
1.0000
100.0%RATEB
1.050OV 0.950UV
2.5
103551
NORHAR#1
2
1.026
141.6
100.6
26% I
41% I
41.2
101.1
29% I
45.7
1.036
143.0
136.8
77.4
1.025
141.5
255.6
1
60.3
171.6
81.3
94.5
36% I
81.4
141.4
140.8
36.3
36.3
48% I
1.035
119.0
48.3
1.030
118.5
1.016
116.8
48.4
1.025
117.9
129026
NRTPTG3
155.3
129329
ELWOOD 2
58.5
1.035
119.0
103171
NWLK HAR
168.8
1.024
141.3
300.0
71% I
49.5R
30.8
304.0
139.8
301.0
N/A
1
28.5
SW
32% I
31.5
103168
GLNBROOK
43.7
171.4
185.0
129342
NRTHPRT2
127.4
129328
ELWOOD 1
CASE 2b: NNC - one cable I/S
Post Contingency loss of Millstone #3
NNC flow reduced to LTE rating
129027
NRTPTG4
144.2
29% I
300.7
N/A
26.5
303.8
300.0
71% I
47.8R
103169
RYTN J A
1
157.2
28.9
1.024
141.4
129024
NRTPTG1
103172
NORWALK
139.3
31% I
SW
30.8
0.0
300.0
70% I
26.5R
299.5
N/A
220.9
98.3
78.4
37.3
97.1
37% I
78.2
37.3
NNC Inter tie (one cable I/S)
301.2
103166
NORHR138
129025
NRTPTG2
1.031
118.5
291.2
45.1
299.2
N/A 299.8
43.9
N/A
301.5
291.2
300.0
70% I
29.6R
N/A
195.3
45% I
45.3
191.1
191.1
97.1
46.4
98% I
43.9
98.3
129344
NRTHPT1
N/A
1.0187
45% I
1
297.9
220.6
78% I
129343
NRTHPT P
44% I
57.6
1
315.9
1.0000
129355
PILGRIM
314.4
58% I
57.6
1.026
141.6
%
58
189.4
46% I
45.5
I
103237
ELYAVE
103173
SASCO CR
168.8
N/A
15.6
35% I
34.9
1.0000
194.5
1.0000
-13.60
1.025
141.5
195.3
23.5
28.2
110.7
28% I
28.2
1.027
118.1
136.1
165.8
N/A
1.0530
159.0
95% I
46.9R
1.0000
1
40.7
1.034
118.9
161.7
103271
RYTN J B
127.0
1.007
18.1
1.031
142.3
103552
NORHAR#2
Bus - VOLTAGE (KV/PU)
Branch - MVA/% OF RATE B
Equipment - MW/MVAR
234.3
234.7
103207
FLAX HIL
43.7
79.7
168.0
100% I
46.9R
174.4
N/A
1.007
20.1
1.0530
75% I
1.0000
100.0%RATEB
1.050OV0.950UV
2.5
103551
NORHAR#1
2
1.026
141.6
111.3
23% I
23.0
42% I
42.0
63.9
34.9
1.035
142.8
139.6
62.5
1
58.5
170.2
74.9
79.2
30% I
75.1
124.6
124.0
30.4
30.4
43% I
1.035
119.0
42.6
1.030
118.5
1.016
116.8
42.6
1.025
117.9