Patent EP-3972102-A1 (EP)
Title: Improvements in or relating to power transmission schemes
Inventor: KUMAR AMIT
IPC: H02M7/483
Filed: 2020-09-22
Abstract: In the field of high voltage direct current (HVDC) power transmission networks, there is a need for an improved power transmission scheme. 
     A power transmission scheme (10) comprises a first DC transmission terminal (12), for connection in-use to a first DC transmission conduit of a DC network, and a second DC transmission terminal (14), for connection in-use to a second DC transmission conduit of the DC network. The first DC transmission terminal (12) is electrically connected with a first DC converter terminal (16) of a power converter (18), via a first electrical interconnection (20), and the second DC transmission terminal (14) is electrically connected with a second DC converter terminal (22) of the power converter (18), via a second electrical interconnection (24). The power converter (18) includes at least one converter limb (26A, 26B, 26C) which extends between the first and second DC converter terminals (16, 22), and the or each converter limb (26A, 26B, 26C) includes first and second limb portions (28A, 28B, 28C, 30A, 30B, 30C) that are separated by a respective AC terminal (32A, 32B, 32C), for connection in-use to a phase (A, B, C) of an AC network. Each limb portion (28A, 28B, 28C, 30A, 30B, 30C) includes a switching valve (34) to facilitate the transfer of power between the DC and AC networks. The or each first limb portion (28A, 28B, 28C), together with the first electrical interconnection (20), defines a respective first DC current flow path portion (42A, 42B, 42C) between the first DC transmission terminal (12) and the respective AC terminal (32A, 32B, 32C). Similarly, the or each second limb portion (30A, 30B, 30C), together with the second electrical interconnection (24), defies a respective second DC current flow path portion (43A, 43B, 43C) between the second DC transmission terminal (14) and the respective AC terminal (32A, 32B, 32C). At least one of the or each first DC current flow path portion (42A, 42B, 42C) includes a series-connected main inductive element (44, 46) and the or each second DC current flow path portion (43A, 43B, 43C) includes a series-connected main inductive element (48, 50). At least one of the first and second electrical interconnections (20, 24) includes a DC circuit breaker arrangement (64; 64') which itself includes at least one auxiliary inductive element (66) that is electrically connected with at least one breaker module (70; 70', 70"). The or each breaker module (70; 70', 70") comprises a breaker switch (72) that is series-connected within the corresponding electrical interconnection (20, 24) and a breaker module capacitor (74) which is connected in series with the auxiliary inductive element (66) to define an auxiliary resonant circuit (76) that is arranged in parallel with the breaker switch (72). The or each auxiliary inductive (66) element is mutually coupled with a main inductive element (44, 46, 48, 50), whereby in the event of a fault (84) resulting in a rising fault current (i 1 ) flowing through one or more faulted DC current flow path portions (42A, 42B, 42C, 43A, 43B, 43C) and the main inductive element (44, 46, 48, 50) therewithin the rising fault current (i 1 ) induces a rising voltage (v 2 ) across the corresponding mutually coupled auxiliary inductive element (66) which creates a growing counter current (i 2 ) in the or each corresponding auxiliary resonant circuit (76). The or each growing counter current (i 2 ) is opposed to the fault current (i 1 ) flowing through the or each breaker switch (72) in the or each faulted DC current flow path portion (42A, 42B, 42C, 43A, 43B, 43C) and thereby permits zero crossing opening of the or each said breaker switch (72) when the counter current (i 2 ) equals the fault current (i 1 ).